The cellular composition of cells collected from the follicular fluid obtained during the IVF procedure and cultured in vitro was examined, as well as the effects of two cytokines, interleukin-2 (IL-2) and tumour necrosis factor-alpha (TNF alpha), on the proliferation of individual cell types. After 48 h in culture, most of the cells were granulosa-lutein cells exhibiting positive staining against 3-beta-hydroxysteroid dehydrogenase (3 beta-HSD). About one-third of the total cell population stained positive with monoclonal antibodies against specific antigen sites on lymphohaemopoietic cells, including B-lymphocytes, T-lymphocytes, natural killer cells, monocytes and macrophages. During this 48-h period, IL-2 and TNF alpha significantly (P < 0.05) increased the proportion of leukocyte common antigen (LCA)-positive cells and monocytes. At the end of 144 h in culture, although LCA-positive cells and monocytes were still present, there were fewer. The main targets for the proliferative effects of IL-2 and TNF alpha in this culture system during the first 48 h are leukocytes rather than steroid-producing cells. Thus, any observed effects from the addition of cytokines in this system may be due to indirect effects of cytokine-activated leukocytes on granulosa-lutein cells.