LPL activity, total lipogenesis and rates of growth were determined for stromal-vascular cells derived from epididymal and inguinal depots of 13 1/2-week-old obese and lean Zucker rats. LPL activity, in cells of both depots, was found to increase between days 4 and 6 and decrease by day 8 in the presence of insulin. Inguinal derived fatty cell LPL activity increased between days 4 and 8 in contrast to lean cells which peaked at day 6 under basal growth conditions. LPL activity was elevated in fatty versus lean cells at days 6 and 8 in inguinal derived stromal vascular cells while in epididymal derived stromal vascular cells, LPL activity was elevated in lean versus fatty derived cells at day 4 and 6 but by day 8 the genotypic effect was reversed. Lipogenesis was elevated in lean versus fatty derived epididymal and inguinal cells at all concentrations of insulin and lean cells showed a dose-dependent response to insulin in contrast to fatty cells. There were no effects of genotype on the proliferative capacity of cells from either depot but some regional differences in growth were observed. These data illustrate that fa gene effects can be studied in primary cell culture.