Thiamin absorption and excretion were assessed in rats with severe folate deficiency (FD) by determining the fate of oral 3H-labeled and intravenous 14C-labeled thiamin over a 6-h test period. Thiamin status was evaluated in these same rats by measuring transketolase activity levels of blood before (TKA) and after (TPPE) addition of thiamin pyrophosphate to the incubation mixture of the assay procedure. Two additional experiments assessed active transport of thiamin and the effect of dietary succinylsulfathiazole (SST) on TKA and TPPE in rats with moderate FD. Intestinal absorption in general and thiamin absorption in particular and thiamin status were unaltered in rats with severe FD. Inanition associated with severe FD may impair thiamin status. Thiamin absorption by active transport was not compromised in FD, and dietary succinylsulfathiazole did not affect thiamin status.