Serum folate and B12 estimations were carried out on 272 admissions to a psychiatric unit during 1972 and 1973. 21–3% had serum folate below 2 ng/ml and 26–1% serum B12 below 150 pg/ml. The organic psychosis patients had a significantly lower mean B12 than the others, and were over-represented among the low B12 group. Low B12 status was also associated with low RBC and WBC. Low folate status was linked with depression, malnutrition, physical illness and low Hb, RBC and WBC. There were more chronic alcoholics than others with serum folate > 4·9 ng/ml, low RBC and macrocytosis. The presence of one or more haematological abnormalities (macrocytosis, low Hb, low RBC or low WBC) predicted low folate in 76%, and low B12 in 79%, but these were also found in 40% of the normal folate and 41% of the normal B12 patients. Macrocytosis may prove to be a reliable sign of alcoholic abuse.