A proportion of the granulosa cells from bovine antral follicles will survive, like stem cells, in anchorage-independent culture. To study these cells, bovine granulosa cells were isolated from medium-sized follicles (3-5 mm), plated out (in aliquots of 2.5 x 10(4) viable cells) onto a 1 mL agar base, and overlaid with 1 mL of methycellulose solution in culture medium (control). The cells were cultured (14 days) and then processed for histology (n = 14) or Western immunoblotting (n = 5). Under control conditions or after treatment with basic fibroblast growth factor (bFGF; 50 ng mL-1), a proportion of the granulosa cells divided to produce colonies; individual cells remained small. bFGF increased the number of cells harvested (15.8 +/- 7.3-fold, as measured indirectly by the relative amount of the nuclear La antigen), increased the average diameter of the colonies from 88.9 +/- 13.5 microns to 136.5 +/- 4.9 microns and stimulated the production of fibronectin 5.7 +/- 1.5-fold (P < 0.05). An extracellular matrix, which has previously been shown to be a basal lamina, was observed in 19.1% of the colonies (total of 350 colonies examined; n = 8 experiments). Cells treated with dibutyryl cAMP (1 mM) hypertrophied and had 50 +/- 28.7-fold and 102.6 +/- 55.8-fold higher levels of cholesterol side-chain cleavage cytochrome P450 (P < 0.001) and 3 beta-hydroxysteroid dehydrogenase (P < 0.01) respectively (n = 5). Thus, granulosa cells with characteristics of stem cells can divide and produce extracellular matrix, or be induced to differentiate when in culture without anchorage.