The relationship between serum calcium and magnesium levels and neuroleptic-induced extrapyramidal symptoms (EPS) was studied in schizophrenic patients. The 16 patients in whom EPS developed had a significantly lower mean drug-free calcium level than the six patients in whom EPS did not develop. In patients in whom EPS developed, drug-free serum calcium and magnesium levels together correlated significantly with the neuroleptic dosage at which EPS first developed; lower calcium and magnesium values predicted EPS at lower dosages. We have previously shown that both serum calcium and magnesium levels were significantly lower during neuroleptic treatment than in the drug-free state. In this study, a similar trend was observed, but the calcium value tended to be, and the magnesium value was significantly lower at the onset of neuroleptic-induced EPS than during the mean of an entire pimozide trial.