Three antioxidant vitamins, the alpha- and beta-carotenes as well as vitamin E, were measured in sera of a normal population in Northeastern Thailand using HPLC. The mean serum beta-carotene level of females was significantly higher than the value for males, i.e, 37.55 (95%CI=34.59-40.51) versus 32.97 (95% CI=30.01-35.93) micro/dl. The beta-carotene level tended to decrease as age increased, particularly in the male population. The mean serum beta-carotene level was also higher in females than in males, i.e., 7.08 (95%CI=6.57-7.59) and 6.26 (95% CI=5.77-6.75) micro/dl, respectively. The average serum alpha-tocopherol (Vitamin E) level of the whole population was 1.08 (95% CI=1.04-1.12) micro/dl and did not show age or sex differences. In general, the serum antioxidant vitamins of smokers were lower than those of the non-smokers but a significant difference was observed only for alpha-tocopherol. Alcohol drinking resulted in slightly lower serum beta-carotene values, whereas coffee or tea drinking and betel nut chewing did not cause any differences with these three antioxidant vitamins. However, we report higher in serum beta-carotene levels of people in Ban Fang district than in Chonnabot district. The results from our study give the base line data of serum antioxidant vitamins in a Thai population and also suggest future intensive study on the relationship of dietary intake and cancer prevention.