"Now is an absolutely ridiculoustime to buy small-cap stocks.

"You'd be a dope to snap up shares of companies like Stone Energy (NYSE: SGY), American Axle & Manufacturing Holdings (NYSE: AXL), Century Aluminum (Nasdaq: CENX), and Sunrise Senior Living (NYSE: SRZ) -- all of which are up more than 500% since March's market low." 

That's what you might be hearing, now that the small-cap Russell 2000 Index is outpacing the S&P 500 by 10 percentage points. Even The Wall Street Journalpredicts that the small-cap rally is set to come to a screeching halt. 

But don't be duped ...
Just because many small-cap stocks have experienced a huge increase in the past few months doesn't mean you should avoid all of them.

First, no one accurately called the market's bottom in March, so it's dubious whether anyone has the ability to call a top just a few months later.

Second, the Russell 2000's sharp rise has largely been driven by the speculative bidding-up of penny stocks(stocks with share prices below $5). Many companies whose share prices exceeded $5 in March have not shared in the astronomically high returns -- including companies whose fundamentals have actually improvedyear to date.

This trend isn't unique to small caps. In fact, S&P 500 stocks whose prices fell below $5 during this bear market -- including Bank of America (NYSE: BAC), E*TRADE Financial (Nasdaq: ETFC), and Advanced Micro Devices (NYSE: AMD) -- have been some of the highest gainers in that index, with each up more than 100% since the bottom.

But this still raises the question: Why have penny stocks risen quicker than non-penny stocks?

Pain, baby, pain
Behavioral psychologists refer to the "pain of paying" -- the mental barrier we face when parting with our cash. The higher the cost, the higher the barrier.

For investors focusing on share price (instead of, say, underlying company quality), it's less painful to toss an extra dime per share into purchasing a penny stock -- even if that dime represents twice what the stock was trading for the day before -- than it is to toss in an extra $5 per share for a stock that was trading for more than $100 a share the day before.

Rational? Certainly not.

However, this speculative irrationality presents the savvy small-cap investor with a great opportunity.

How to cash in on small-cap movement
There are two ways you can profit from the rush to penny stocks:

1. Join the rush, and wager your hard-earned money by guessing which penny stock might rise next.

2. Invest in small-cap companies whose fundamentals have been improving, but which are still undervalued by the market.

As much as we'd all love to have a stock shoot up nearly 4,500% in just a few months -- as penny-stock micro-cap Diedrich Coffee recently did -- at the end of the day, the first tactic is nothing but a risky crapshoot.

So though your inclination might be to go for the gusto to make up for losses, the second option is really the only way to set yourself up with a portfolio that will grow your wealth at above-average rates over long periods of time. Continued...