Sixteen chronic schizophrenic subjects were treated for 3 months each with either a benzo-pyrone (Paroven/Venoruton, Zyma) or a placebo in a randomized, double-blind crossover trial. They continued to take their previous drug therapies. Therapeutic effects were measured by the Brief Psychiatric Rating Scale (BPRS), by self-assessment, and by assessment by a relative. Eleven patients completed the trial in relation to BPRS assessment. When on the active substance, as compared with the placebo, they showed a mean improvement of 27% (significant at the 1% level). Ten patients completed the trial in relation to the self and relative's assessments. There were improvements of 16% and 13%, respectively (significant at the 5% levels). Half the patients showed improvements on all the tests. Their improvements were 49%, 31%, and 21%, respectively. There was evidence that the active substance began to have an effect within 2 weeks. No side effects were observed with the active substance.