<p>I think that if you truly think you can study for it and do well, then you should go for it. I have not a clue about taking two tests, because I only have to take the GRE and the GRE Lit test and there is not one for my other major (Theology). All I know that for the Graduate Schools, you just have to try your best and do everything you can do! SO, if you think you can do it, then study for it and do it!</p>
<p>I really wouldn't advise taking two tests. First, they're very expensive! Second, they are offered very few times a year -- you would have to take one in April of your junior year and the other in November of your senior year if you were determined to take both.</p>
<p>There are more productive ways to use your time and money, particularly since most molecular/cellular biology schools do not weight the subject test very heavily. (It's optional for almost all of them.) The only school that really cares about the subject test is UCSF, and they only care that you're in or around the 90th percentile.</p>
<p>Just take whichever single test on which you feel you will perform best.</p>