Voice and speech changes as a result of clinical treatment for 17 depressive and 15 schizophrenic patients were investigated. Speech samples taken at interviews before and after treatment were analyzed with regard to f0, spectral energy distribution, and formant frequencies of vowels occurring in identical phonetical context. Both groups of patients showed a decrease in f0 after therapy, which was interpreted as a reduction of general arousal. Differential results with regard to spectral energy distribution suggested that the voice of depressives became more relaxed after therapy, but the opposite seemed to be true for schizophrenics. Significant formant changes obtained for the first formants of two vowels were interpreted as differences in the precision of articulation before and after therapy.