The thiamine pyrophosphate (TPP) effect and erythrocyte transketolase activity (ETKA) in a group of 28 patients admitted to a psychiatric emergency ward because of severe alcohol withdrawal syndrome were compared with the TPP effect and ETKA in a control group of 20 healthy nonalcoholic volunteers. The patients were treated with 300 mg thiamine 3 times daily as intramuscular injections, and the TPP effect and ETKA were measured after 1 and 4 days of treatment. No difference was found between the patient group and the control group with regard to the TPP effect and ETKA and no decline in the TPP effect was found in the patient group after 4 days of intensive treatment with thiamine. ETKA increased with intensive thiamine treatment, which suggests that ETKA is a sensitive indicator of thiamine deficiency. Serum magnesium, which is a cofactor for thiamine pyrophosphate, decreased significantly with the disappearance of alcohol from the blood in patients with high initial blood alcohol levels, but this shift did not interfere with biological thiamine activity.