Rat heart and spleen slices were incubated with 3,4-dimethoxyphenylethylamine-1-14C(14C-DMPEA) in Krebs medium at 37 C. At the end of 5-20 min of incubation, the heart did not take up the radioactivity while the spleen did. The Km and Vmax values of uptake in the spleen were 1 x 10(-4) M and 20 nmole/g per min, respectively, and the uptake was reduced to 16.0-35.1% in the cold (4 C) and to 40.3-64.0% in Na+-free medium. Thus, the uptake was an energy-dependent active process but was only partially Na+-dependent. Spleen slices incubated with 14C-DMPEA-free medium for 15 min following incubation with 14C-DMPEA retained 41.0-74.8% of radioactivity. The uptake was insensitive to norepinephrine (0.313 and 0.939 muM), dopamine (9.98 muM), 5-hydroxytryptamine (5 muM), cocaine (14.8 muM), 1-amphetamine (0.3 and 300 muM), d-amphetamine (300 muM), and normetanephrine (45.7 muM). 6-Hydroxydopamine treatment of rats, which produced 93% reduction in the splenic norepinephrine content, did not significantly reduce uptake. Thus, the uptake of DMPEA into the spleen is not by adrenergic neurones.