The responses at the Ishihara test, the Nagel anomaloscope, the standard Panel D–15 and the 100 hue test (with correction of the age effect) were recorded in 38 alcoholics in deprivation period (successively subdivided according to age, to abstinence duration and to liver condition) and in 32 subjects suffering from mental diseases (successively subdivided according to ethylic past, to age, to duration of the stay in the hospital and to activity). It is shown that alcoholism causes a diminution of the performance at the used colour vision tests and especially at the 100 hue test. The defect can be ascribed to psychical factors (chiefly in the cases of mental disease and in the younger people), but also to an acquired blue-yellow defectiveness of colour vision with a shift of the Rayleigh match to red (such a defectiveness can also be due to a liver damage and to some intoxications) and even to a Type II acquired red-green defectiveness of colour vision (possibly by tobacco or disulfiram intoxication). The defect due to alcohol itself soon disappears during desintoxication. The authors draw some practical conclusions.