Synaptosomes of corpus striatum of rats were incubated at 37 degrees C in a medium containing a tracer concentration of 14C-dopamine. The uptake of 14C-dopamine was significantly inhibited by 2,4-dinitrophenol and by lowering the temperature, while morphine (10 mumol/l) was without effect. In another series of experiments, the K+-induced (53 mmol/l) increase in overflow of 14C during superfusion of the synaptosomes previously equilibrated in 14C-dopamine was measured. 10 mumol/l morphine did not affect the overflow of radioactivity, while 50 mumol/l slightly inhibited it. This inhibition, however, was not antagonized by an equimolar concentration of naloxone. In contrast to previous studies in striatal slices, we could not observe any opiate-specific effect on K+-induced release of labelled dopamine in striatal synaptosomes.