Malononitrile administered intravenously in doses varying from 2-4 mgms/kg body weight was of no benefit in the treatment of 9 patients who received approximately the amount of malononitrile recommended by Hydén and Hartelius. With the exception of a mild toxic reaction after injections the patients displayed no improvement of their psychotic conditions. In addition, no alterations were observed in their emotional reactions. Our investigations were carried out predominantly on schizophrenic patients. The material on manic-depressives is insufficient from which to draw conclusions. The theoretic concept of Caspersson and Hydén concerning the relationship of nucleoprotein metabolism and malononitrile was not investigated at this time. We were interested in the clinical application of malononitrile which, as our reported findings show, is essentially negative.Abstract Teaser