The locomotor activity of rats subcutaneously treated with apomorphine HCl (300 microgram/kg, 30 sec before emmission into actometers) was evaluated every 60 sec for 1 hour. An inhibitory phase appeared in the first 6 min of recording in comparison to the more elevated values of the control group. From 18th to 44th min a more sustained activity was easily recognizable in treated rats in comparison to the decline of control values. The results were discussed by supposing that the first amounts of drug entering CNS stimulated pre-synaptic dopamine receptors and the full dose activated post-synaptic dopamine neurons. The study of time-course of a single dose of apomorphine could be a useful model for evaluating pre- and post-synaptic effects of antidopaminergic drugs.