Past studies with animals have demonstrated that 4-ami-nobiphenyl (ABP) administration results in the formation of appreciable amounts of adducts between the carcinogen and both serum albumin and hemoglobin. The hemoglobin adduct is relatively stable in vivo, but may be readily hydrolyzed in vitro to regenerate ABP. The formation of this adduct reflects a mixed-function oxidase-mediated metabolic pathway operating directly on the amine. The predominant albumin adduct, 3-(tryptophan-Nl-yl)-4-acetylaminobiphenyl, reflects the contribution of N-acetyltransferase activity as well as mixed function oxidase activity to the overall metabolism. The simultaneous measurement of these two different adducts thus offers an opportunity to investigate the role of both ABP and acetylator phenotype in bladder carcinogenesis. An analytical method, using gas chromatography coupled with electron capture detection, was developed to quantitate ABP adducted to hemoglobin.