Isolated morphologically normal bovine preantral follicles (40 to 70 microm) were cultured for 8 d in collagen gel in control medium or in 1 of 3 conditioned media from the murine granulosa cell lines GRMO1L, GRMO2 and GE2. The percentages of follicles at Day 1 that remained nomal at Day 8 were similar for follicles cultured in the conditioned and control media (84 to 90%). A significantly higher percentage of follicles cultured in each of 3 conditioned media started to grow (89%; P < 0.05) and their increase in diameter was greater than that of follicles cultured in control medium (72%; P < 0.05). The mitotic activity of the granulosa cells from follicles cultured in conditioned media was increased (P < 0.05) indicated by a higher percentage of nuclei that incorporated BrdU compared with that of follicles cultured in control medium. Follicular viability was measured by the presence of nonspecific esterase activity, active mitochondria and dead cells in cultured follicles using the fluorescent probes calcein-AM, rhodamine 123 and ethidium homodimer-1 in combination with confocal laser scanning microscopy. The percentages of follicles with esterase activity and active mitochondria present in their granulosa were similar for follicles in all groups. Culturing in GRMO2 or GE2 tended to lower the number of granulosa with dead cells. The percentage of follicles with oocytes without esterase activity and active mitochondria was lower (P < 0.05) in follicles cultured in GRMO2 or GE2 compared with those cultured in control medium. Moreover, the percentages of dead oocytes tended to be higher in follicles cultured in GRMO1L and GE2 compared with oocytes of follicles incubated in control medium. Taken together, the conditioned media stimulated follicular growth and granulosa viability as well as enhance mitotic activity of the granulosa cells. However, they negatively affected oocyte viability.