The educational "pipeline" that provides tomorrow's scientists and engineers leaks far more females than males, particularly in the junior high age range. The reasons for this are complex and still being studied. However, by college age, the gender differences seen at earlier ages seem to narrow or disappear when one considers only those students who are high achievers or who are enrolled in upper-level science courses. In the field of biology, women now earn half or more of the baccalaureate degrees and comprise half of the graduate student population. There may be a loss of females in the sciences, but whatever the causative or discouraging factors are, they apparently do not operate in biology, at least through the college level. Biology seems to be a gender-neutral science through the mainline educational system. Do females and males choose science for different reasons? This article describes the results of a survey conducted among college students in the gender-neutral field of biology to learn when they became interested and what factors determined their origin and maintenance of interest in biology. Males' and females' reasons for choosing science were different, but students of both genders can be supported if instructors are aware of and account for their different motivations. (Contains 1 figure and 2 tables.)