The dibenzothiepine zotepine is a new potential "atypical" neuroleptic exhibiting powerful antiserotonergic and antidopaminergic properties. The efficacy of zotepine was evaluated in a double-blind controlled trial versus the tricyclic neuroleptic perazine in 41 patients suffering mainly from the paranoid-hallucinatory type of schizophrenia. The key outcome variable was the extent of mental disturbance as defined by the total score of the BPRS. Additional outcome variables were GAS and CGI. In addition, adverse reactions and extrapyramidal side effects were assessed according to the FSUCL scale and the Gerlach and AIMS rating scale, respectively. Additional variables recorded were blood pressure, heart rate and routine laboratory parameters as well as electrocardiogram and electroencephalogram. In the first two days, standard equivalent doses of both drugs were administered. Thereafter, doses were administered as required. The efficacy of both substances was compared after 7, 14 and 28 days of treatment. Both drugs showed a similar antipsychotic efficacy. Under zotepine treatment a 55% improvement of the BPRS total score was observed while perazine led to a 41% BPRS score reduction. After 7 days the zotepine group was significantly more improved than the perazine group, possibly due to a dosing effect in the perazine group. In the zotepine group, fewer adverse reactions and a better benefit/risk index were observed although the differences between the two treatment groups did not reach levels of statistical significance. There were no drug-specific abnormal laboratory findings. Thus, in the present study there was no significant difference between zotepine and perazine with respect to antipsychotic efficacy and side-effect rates. However, zotepine showed a trend to a better benefit/risk index at the end of treatment.