Aflatoxin-albumin (AFB-albumin) adducts and hepatitis B markers (anti-HBs, and anti-HBc) were measured in vegetarians and nonvegetarians from Chiang Mai, Thailand. The AFB-albumin adduct levels were detected in 62% (37 of 60) of the vegetarian samples and 22% (22 of 100) of nonvegetarians. Somewhat higher levels were detected in vegetarians sera collected in the summer than in the winter, although this difference was not statistically significant. Subjects who were hepatitis B surface antigen (HBsAg)-positive had slightly higher AFB-albumin adduct levels than subjects who had evidence of past exposure (anti-HBc-positive) or no HB virus infection. This study indicated that vegetarians may have a higher frequency of aflatoxin exposure than nonvegetarians. Thai vegetarians consume various vegetables, grains, peanut, soybean, and fermented products, which have been reported to be sources of aflatoxin.