SummaryUsing the colorimetric method outlined by Cabaud, the author has studied 330 patients with miscellaneous diseases. The results agree with previous papers. The literature is discussed. Beside the well known clinical interest of the transaminase activity in the blood, many facts ask for more extensive research, particularly as far as brain and kidney diseases are concerned. Other transamination systems, as thyrosine-glutamic transaminase could prove to be of clinical interest.