Folate (RBC, serum, CSF) and B12 (serum and CSF) and 5-HIAA and HVA (CSF) concentrations were measured in patients with senile dementia. Those with RBC folate < 130 ng/ml. were given folate/B12 in a double-blind crossover trial. (1) Amine metabolites and folate were unrelated. (2) CSF folate levels rose significantly but slowly on ward diet only independently of the period of intensive replacement. (3) There was no clinical improvement over the 24 weeks of observation but in view of the biochemical findings the period of study may have been too short.