Many schools want to see LORs from science professors. I would give an example from Columbia: "Three CONFIDENTIAL letters of recommendation from science professors or one composite letter from a pre-health committee." This requirement is a little bit broad, I think. For example, I was doing undergraduate research for one of the professors in Oral Bio department. I did not take any classes from him because he only teaches graduate courses. He knows me real well though. Would a letter from him be considered one of the required "science professors" letters? I am guessing my question could be only answered if I actually go and call each of the schools I plan to apply to. But if you have input or have dealt with such a problem, you are welcome to let me know Thanks!