the supravital stain with tripan blue (at) was used for differentiating live bovine immature oocytes from dead ones. it is important to know the viability of the oocytes, in order to discard the dead ones before the in vitro fertilization (fiv). smaller than 6 mm follicles were punctured, from ovaries obtained from an abattoir. the cumulus oocyte complexes (coc) were classified as a, b or c. only those of quality a or b were taken into account. two categories were formed (autumnwinter and spring-summer) and 4 groups within each category were considered: a control group (cg), which was not stained with at and three groups: g1, g2 and g3 stained with at for 2, 5 and 10 minutes, respectively. blue stained coc (dead) were discarded, live coc were cultured for 22 h in a maturation culture and were stained again, maintaining the same exposure times. insemination was then performed and compact morules counted, in order to evaluate the efect of at and season. in conclusion, at stain can be used up to 10 minutes to differentiate live and dead oocytes, without any deleterious effect on the gametes.