SUMMARYIn two cases of chronic schizophrenia complicated by diabetes mellitus, the concomitant use of the neuroleptica and oral antidiabetics was attended by the appearance of symptoms simulative of syndrome malin, i.e. hyperpyrexia, tachycardia, blood pressure instability, disturbances of consciousness, muscle rigidity, tremor, dysphagia, salivation and urinary incontinence. In one of these cases, the patient, a 47‐year‐old man, died 10 days later. In the other case, a 62‐year‐old woman, almost all the symptoms subsided after 14 days, and oral dyskinesia persisted for only one additional month. In both cases, hypoglycemia due to oral antidiabetics was not seen. In Case 2, a combined regimen of oral antidiabetics and neuroleptica was later resumed. Again, a similar set of symptoms as seen initially were noted, along with an elevation of the serum CPK level. Parenterally administered biperiden proved to be highly effective in the control of the symptoms. The pathogenetic mechanism of these symptoms might possibly be explained as potentiation of the action of the neuroleptica by oral anti‐