Press releases and lots of chatter are all well and good, but nothing speaks louder than real investors investing real money in a certain stock. With that in mind, here are last week’s small-cap stocks with the most buying activity. We’ve analyzed the reason behind the mass purchasing below, as well as what the future may hold in each case.

In no particular order, last week’s most-purchased stocks were Antigenics Inc. (AGEN), SpongeTech Delivery Systems, Inc. (SPNG), Hemispherx Biopharma, Inc. (HEB), and Satyam Computer Services Ltd. (SAY).

Oh, and just for the record, Bank of America (BAC) saw the heaviest accumulation of all stocks.

Antigenics Inc. (AGEN)

Here’s a little irony for ya’… last week’s first op-ed headline for Antigen was the Motley Fool’s “1 Star Stocks Poised to Plunge”. The worry was that AGEN’s 200% gain from the week earlier was going to be retraced.

Well, it wasn’t.

Instead, this penny stock flattened last week, which is considerably better than a selloff, but not as good as more gains.

As for the reason Antigen rallied, the stock was riding the coattails of a broad biotech surge. However, Antigen does have something in development that helped spur the stock - last week, the company’s kidney cancer therapy Oncophage was indeed shown to extend the lives of its users (though it’s only approved in Russia, and is waiting for approval in Europe).

So, buy or sell? I say sell while there’s something to gain.

Not only is the failure to follow through on the prior week’s surge a red flag, but there are some interesting tidbits about Oncophage the market seems to have forgotten.

First, though Oncophage is approved for sale in Russia (as of a year ago), it’s not actually on the market there. What the heck? Second, Oncophage went through the FDA’s Phase III testing as a kidney cancer treatment here in the U.S., but was ultimately a failure in their eyes - not approved. There are other possible uses, but nothing past Phase II testing.

If you don’t mind past and future losses, AGEN is great. If you actually want your investments to be, you know, profitable companies, steer clear. We’re not sure why the buying interest was so heavy last week.

SpongeTech Delivery Systems, Inc. (SPNG)

We’ve been following this penny stock since it was trading around five cents in mid-May.Wait, strike that - we’ve actually been following it since lare 2007…. it just didn’t get interesting until May of this year. However, our readers who stuck with it from our 2007 recommendation finally made a lot of money. Anyway…

We also encouraged traders to take profits at 8 cents, and again at 20 cents (which we also thought was fair value at the time). As it turns out, we were a bit early - about a day - on calling the peak, but Friday’s huge pullback from the peak at 28 cents (to the close of 17 cents) proves the discipline we were trying to apply….it’s better to be early than late, ’cause the tumbles come a lot faster than the rallies.

As for why SPNG has done so well of late, it’s because the company pre-reported more than $50 million in revenue and more than $10 million in earnings for the last fiscal year. Not bad for a company that was at a market cap of $30 million two weeks ago.

The problem is, the company was valued at $100 million when the full-year news came out, and was at $123 million when news of $6.4 million worth of orders was announced. Congrats to the company, but it’s all priced in…. the growth pace is slowing, and the euphoria is wearing off.

There’s a future for the company, but since SPNG is likely to be fully valued now, we still think it’s wise to lock in profits.

Hemispherx Biopharma, Inc. (HEB)

This is hardly the first time Hemispherx was put on our radar. Last week’s accumulation was a carry-over from the prior week’s hope that chronic fatigue syndrome treatment Ampligen would finally be approved by the FDA. It’s still not, pushing the FDA’s announcement delay now past the two-week mark. Very unorthodox.

In the meantime, the cash-desperation started to shine through.

The company tested the waters to see if enough money could be raised through a private placement (PIPE), but the response was tepid. The next option is/was to issue a registration statement for $150 million worth of shares…which couldn’t be sold by the buyer for six months from the date of issue. Our understanding is that the possibility still exists, but is going to be equally tough to sell as long as the FDA decision is still unannounced.

The whole thing stinks. If Ampligen was approved, the company could raise all the funds it needed. Why such a rush to raise funds (with much fewer selling points) before the FDA’s decision?

We’ve heard multiple whispers that professional pumpers are working this stock, which makes sense - keep the price afloat when you’re trying to raise funds. What happens afterwards though?

We don’t think anything else Hemispherx has got in the pipeline can justify a share price of $2.67, making this one a ticking time bomb in our view.

Satyam Computer Services Ltd. (SAY)

It’s back. Tuesday and Wednesday were banner days for this Indian tech stock, pushing shares from $2.72 to $4.94 on the best buying volume we’ve seen in months (prior to the $ billion accounting BS fiasco from January). Unfortunately, Thursday’s and Friday’s selling was pretty strong as well, pulling SAY back down to $3.67. Net, however, it was still one of the market’s most-bought stocks.

But why the rally? Most of it as attributable to a flattering ‘overweight’ rating from J.P. Morgan. The report’s target price for shares was only $2.10 though, so why blow past the $4.00 mark (even temporarily)? The outlook for 2010 is much better than current or past results.

Our take? It’s actually a decent calculated risk, not to mention a stock that’s under-followed. Plan on lots more volatility, but we don’t think this is a totally crazy long-term idea here.

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