Total thiamine, free thiamine, thiamine diphosphate (TDP) plus thia-mine triphosphate (TTP) and total hydroxyethylthiamine (HET) levels were measured in brains of control, deficient, and oxythiamine (OTH)- and pyrithiamine (PTH)-treated rats. The brain levels of TDP+TTP decreased to 39% and 12% of the control thiamine levels in defici-ent and PTH-treated rats respectively. The brain HET and TDP+TTP levels of the OTH-treated rats were not significantly different from the controls. The HET levels were decreased significantly (α<0.005) by the fourth day of treatment and decreased steadily to 1/7th of the control values in the terminal stages only in the PTH-treated rats. A significant drop in the HET levels from the control levels was interpreted to mean that the pyruvate utilization was significantly impaired in the brain.