Psychophysical pain ratings and somatosensory evoked potentials (EPs) were studied in 17 off-medication patients with schizophrenia and 17 age- and sex-matched normal controls. Five of the 17 schizophrenic patients also participated in a clinical trial of naltrexone. In comparison with normal controls, schizophrenic patients were significantly more insensitive to painful stimulation (based on nonparametric analogues of d'from signal detection analysis) and had significantly smaller somatosensory EPs to painful stimuli. Schizophreniucs treated with naltrexone showed significant increases in EP amplitude at higher stimulus intensities and hyperalgesic effects on pain ratings.