Trying to find a reasonable entry point for investing in the biotech sector, which is shooting skyward again after an early spring sell-off that halved the sector's market capitalization, seems nearly as arduous a task.

Just ask the investors who poured $2 billion into Janus Global Life Science Fund in February - no doubt having noticed the 100% return of the previous three months - just before the sector tanked and the mutual fund fell by 30% in March. In similar fashion, investors threw money at mutual funds such as Fidelity Select Biotechnology and Rydex Biotechnology, which plummeted 30% and 27%, respectively, in March.

But the recent rally shows that investors weren't scared off by the plunges, despite genuine reason to be nervous. "There's an incredible amount of optimism about the human-genome project, and there's probably money to be made, but it's unclear when it's going to be made," says Emily Hall, an analyst who follows biotechnology funds at researcher Morningstar Inc.

But if biotechnology does hold great promise, how should an investor get exposure, especially given the volatility? It depends on your stomach for roller-coaster rides. If risk averse, says Faraz Naqvi, manager of Dresdner RCM Biotechnology Fund, "I wouldn't invest in a biotechnology fund." Whatever their tolerance, individuals probably shouldn't put more than 5% of their investment portfolios into the sector, he adds.

If you do want to roll the dice, says William Dougherty of Kanon Bloch Carre, a retirement-plan consultant, "I'd stick with a pure biotechnology play," partly because "it's a way of controlling what you're after." Buying a diversified fund for its biotech exposure, he says, means you only stay exposed for as long as the manager likes the sector. Morningstar's Ms.

Hall suggests sticking with funds and managers with long-term records and experience in the sector. She says Fidelity Select Biotechnology, like many of Fidelity's sector portfolios, tends to switch managers frequently, but is a good option because it has Fidelity's vast research resources behind it. Rydex Biotechnology, she says, is also a good option because it is index-based and gives investors broad exposure to the sector. Among the broader health-care portfolios that have exposure to biotech, Ms. Hall likes Scudder Health Care Fund.

Regardless of what strategy a mutual-fund investor follows, history shows that market timing is particularly difficult in biotech.