In nine schizophrenic patients on drug holiday, growth hormone (GH) response to apomorphine HCl 0.75 mg (APO) was compared with normal control data. Patients were tested at two month intervals for up to 14 months. Seven patients relapsed, and of these, five had exaggerated GH responses to APO at that time. Of these five, three had exaggerated GH responses to APO prior to clinical deterioration. Further work is required to determine whether this test can be a useful predictor of relapse.