Accumulation of radiolabeled pantothenate by isolated adult rat adipocytes was studied in an in vitro system. Maximal uptake after 1 hour incubation occurred in media containing 0.03 mM pantothenate, about 100 picograms (pg) per adipocyte and was less than 1 pg per cell. Using such saturation conditions, uptake was energy- and temperature-dependent, with about 50% maximal accumulation occurring after 5-10 minutes incubation. Uptake was decreased by the addition of unlabeled pantothenate, but not other water-soluble vitamins. The serum level of pantothenate was decreased about 25% in animals 23-25 months old compared to those 11-13 months old, yet the ability to accumulate pantothenate at saturation conditions by adipocytes was no different. These data suggest that cellular accumulation of this vitamin is specific and that the capacity to do so under optimal conditions does not change with advancing age in this system. It is not known whether in vivo suboptimal or altered rate of cellular pantothenate uptake occurs with aging, or if it remains unchanged and lower serum levels are the result of decreased dietary intake.