The author performed a clinical study of 492 depressive, 127 manic and 46 double phases in 150 patients with manic-depressive psychosis where the disorder manifested itself after the age of 40 with an average duration of the disease of about 10 years. Some general regularities in the syndrome formation and syndrome modifications of the depressive (from subdepressive to endogenous, anxious and delusional depressions) and manic (from hypo and endogenous mania to angry, aproductive mania with pseudoparalytical and senile like traits) syndromes were displayed. It was demonstrated that supplementary factors facilitated such changes as well. The acheived data permitted to qualify longitudinaly more precisely the manic-depressive psychosis during involution as well as to determine the frequency of separate symptoms in each depressive or manic phase.