Spleens of mice treated with 9-beta-D-[2,8-3H]arabinofuranosyladenine (araA), 0.5-30.0 mg/kg showed rapid dose-dependent accumulation of 3H, which peaked at 2.5 mg/kg. Lymphocytes from spleens showed linear uptake when incubated with 0.68, 1.36, and 5.03 microM araA over 120 s. With 1.0 mM araA, uptake was reduced in rate but was not saturated. Tritiated metabolites identified from these lymphocytes were araA which predominated after brief incubations, its deaminated form (araH), and some phosphorylated product in small amount. Inhibition of deaminase increased intracellular araA. Although potent inhibitors of nucleoside transport inhibited araA uptake marginally, adenosine competed with araA for about 50% of the uptake capacity. The data suggest that the uptake of araA by mouse lymphocytes, which is not simple diffusion, occurs by a mechanism distinct from typical nucleoside transport.