Exposure to aflatoxin B1 (AFB1) is one of the major risk factors in the etiology of human hepatocellular carcinoma (HCC). The development of highly sensitive and specific methods for detecting AFB1 and its macromolecular biomarkers are critical for identifying individuals at risk for hepatocellular carcinoma. The detection of aflatoxin-albumin adducts (AFB-ALB) in serum has been used to investigate the relationship between aflatoxin exposure and HCC. A more sensitive and reliable method to detect AFB-ALB in serum was modified by separating serum albumin with Microcon-50 microconcentrators in stead of using precipitation. The method could separate serum albumin quickly and make protein digested in the same container. Thus, the step for transferring samples was reduced and recovery rate was improved. The AFB-ALB adducts were then determined by radioimmunoassay. The AFB-ALB adducts of human serum samples from Qidong, Jiangsu Province, and Fusui, Guangxi Zhuang Autonomous Region of the People's Republic of China were detected. The results indicated that the exposure of AFB1 is common and the positive rate for AFB-ALB adducts in serum of these populations is high.