The AA. report on the eegraphic, behavioral and neurovegetative effects caused by the i.v. administration of mianserin, in the rabbit. This substances induces behavioral sedation and EEG synchronization. In addition, these changes are partially reinforced with L-5-hydroxytryptophan (L-5HTP) and inhibited by pretreatment with DL-p-chlorophenylalanine (PCPA). In the light of these data, the AA. discuss the possible interactions between mianserin and neurotransmitter systems, particularly the serotoninergic one.