AbstractSubpopulations of granulosa cells of differing responsiveness to epidermal growth factor (EGF), fibroblast growth factor (FGF), pituitary gonadotropin preparations, and rat erythrocyte suspensions (RBC) have been detected using an anchorage‐independent clonal agar assay. All growth factor preparations were capable of enhancing colony formation when added alone, and elicited cloning efficiencies as high as 35% when added to the culture system at optimal concentrations in a variety of combinations. The FGF preparation was the single most effective stimulator of colony formation, augmenting both colony numbers and colony size at concentrations as low as 50 ng/ml. However, unlike the other growth factors in this assay system, a plateau in responsiveness could not be reached even at levels as high as 1 μg/ml. NIH‐FSH‐P2 and NIAMMD‐bLH‐4 were considerably less potent than other growth factors. Both preparations were inactive at concentrations less than 1 μg/ml and produced an optimal response