This paper discusses conceptions of identity in relation to science education and presents material from a series of interviews and focus groups with graduate students in science and technology. Given difficulties in retention and levels of significant participation by minority students indicated by aggregate data, the issue of race, as it informs critical interactions at a majority research university, is explored in terms of its effects on identity formation. It is argued that we need to look at "real-time" science to see how subtle interactions affect minority graduate students. These interactions reveal how identity is established through the positioning inside or outside of the laboratory culture. Three themes were explored regarding the tensions of identity formation in the context of race and science education: (1) the issue of isolation, marginalization, and invisibility; (2) being valued through recognition of one's contributions to the community of scientists; and (3) reading race as an additional burden for minority students. Two participants' stories and their positioning as outsiders are explored in detail. The authors contrast building an identity as a scientist through one's educational experiences against being positioned as the "only one" representing his or her race at a primarily White institution. (Contains 1 table and 3 footnotes.)