The effects of chronically administered phenothiazine medication upon aspects of skin conductance (SC) and heart rate (HR) in 32 schizophrenic patients were assessed in two ways. Skin conductance scores obtained during rest and during the performance of a series of span of apprehension tasks were correlated with a phenothiazine dosage index (PDI), representing chlorpromazine equivalent daily dosage. For 15 schizophrenics withdrawn from medication for 3 months and for nine normal controls pre- and postwithdrawal rest and performance scores were obtained and compared by repeated measurement analyses of variances. Results, congruent with other studies, indicate that phenothiazines reduce SC level, elevate HR and restrict frequency of specific and nonspecific reactivity in SC and range of variability in HR. Moreover, it was shown that several of these effects are linearly related to daily dosage level. The implications of these findings for past and future uses of autonomically mediated psychophysiological variables in the study of phenothiazine-treated schizophrenic disorders are discussed, as well as the applicability of the PDI in controlling statistically drug dosage-contaminated psychophysiological variance.