Follicles were isolated from the ovaries of 10-day-old C57BL6/CBA F1 hybrids by mechanical and enzymic treatment, embedded in a collagen-gel matrix to maintain the 3 dimensional integrity of the follicle and cultured for up to 14 days. Gels were removed at various times during the culture period and prepared for histology. Follicles grew from unilaminar to multilaminar stages within 6 days of the culture period. A more detailed assessment of growth by counting follicles at different stages and measuring oocyte and follicle diameters showed that follicle growth was maintained for up to 14 days in culture. Initially the proportion of unhealthy follicles was high but this declined after 6 days in culture.