Vitamin Bl2 and folic acid concentration in blood serum was measured in 116 psychiatric inpatients, 32 healthy controls, and 21 neurotic patients. Vitamin B12 deficiency was found in 46 (39.7%), 5 (15.6%) and 2 (8%) subjects, respectively, while folic acid avitaminosis in 23 (19.8%), 0 (0%) and 1 (4.3%) patients, respectively. The majority of intergroup differences were highly statistically significant (except for the prevalence rate of folic acid avitaminosis in psychotic an neurotic patients). Higher rates of avitaminosis prevalence were correlated with older age, elementary education and Carbamazepine treatment, either jointly with a neuroleptic drug or as the only medication (in the case of vitamin B12). Type of mental disorder (psychotic vs. neurotic) had 110 significant effect either on the frequency of avitaminosis or on the mean level of the vitamins concentration.