Changes in the blood picture as well as in the content of folic acid and iron in the serum were investigated in 223 patients treated in a psychiatric clinic because of psychoses and dementia. Psychopharmaka of the phenobarbiturate type, dihydrophenytoine as well as primidone were administered in 29 cases. As anaemia could be identified in 32 patients; 3 of them turned out to be a hyperchronic anaemia, 25 a normochromic anaemia and 4 a hypochromic type one. In 78.1% of the anaemic patients there was a lowered folic acid level. All four cases with hypochromic anaemia showed a lowered serum level. A hypersegmentation of neutrophilic granulocytes could be identified in 48 patients (28.4%), with a lowered folic acid content in the serum being present in all cases. A lowered folic acid content in the serum could be found in 76.2% of the patients. All patients treated with psychopharmaka showed a subnormal folic acid content. On the other hand, a lowered iron content in the serum could only be identified in 8.1% of the cases. The final evaluation of all findings gathered results in the recommendation to attach greater importance to a direct determination of folic acid concentration in the serum in those cases of disease particularly exposed.