A cross-sectional study was carried out among 39 current smokers (CS) and 60 noncurrent smokers (NCS) to evaluate the effects of cigarette smoking on folate and vitamin B-12 concentrations in the circulation and in tissues directly exposed to cigarette smoke. Univariate analysis showed significantly lower plasma, red blood cell (RBC), and buccal mucosa (BM) folate and BM vitamin B-12 concentrations in CS compared with NCS. The association between smoking and folate and vitamin B-12 concentrations in plasma, RBCs, and BM cells was reduced after other variables were controlled for. Total folate intake and plasma vitamin C concentrations were significant predictors of plasma and RBC folate concentrations. The plasma and RBC concentrations of folate were significantly lower in subjects who had last smoked < 1 h before the blood sample was drawn than in subjects who had smoked earlier. At the current recommended dietary allowance (RDA) for folate, CS had 42% lower plasma folate concentrations than NCS, whereas at an intake three times the RDA, the plasma folate concentration was the same for CS and NCS. The results also suggested that CS have BM folate and vitamin B-12 concentrations that are lower than those of NCS.