Unusually frequent sinistral motor and sighting dominance have sometimes been reported in schizophrenics, although the majority of patients are still dextral. In this study, assessment of lateral dominance also included a measure of grip strength--a potentially more sensitive index of dominance or lateralised impairment; schizophrenics, non-schizophrenic patients (affective disorder), and normal controls were studied. There were no differences in handedness or sighting dominance. Affective patients, particularly bipolar psychotics, had greater right-handed grip superiority than normals or non-paranoid schizophrenics. Paranoid schizophrenics were similar, being significantly greater in right-sided dominance than non-paranoids, who tended toward a smaller value than normals. Hand grip asymmetry was highly correlated with handedness in normals, but not in patients. The possibility is discussed that these results may reflect asymmetrical patterns of cerebral impairment or attentional bias.