The concentrations of 2-amino-3-methylimidazo(4,5-f) quinoline (IQ) and 2-amino-3,8-dimethylimidazo (4,5-f) quinoxaline (MelQx), a family of mutagenic and carcinogenic heterocyclic amines, in the plasma of normal subjects (10 cases), patients with uremia receiving maintenance hemodialysis treatment (9 cases) and patients with uremia just before induction of hemodialysis treatment (5 cases) were determined by a high-performance liquid chromatography method. The plasma levels of IQ and MelQx in uremic patients just before induction of hemodialysis treatment were 12.6 ± 4.1 nM (mean ± S.D., n = 5) and 10.0 ± 2.3 nM (n = 5), respectively. In patients with uremia receiving maintenance hemodialysis treatment, IQ and MelQx were detected in 4 and 2 out of 9 cases, respectively and the levels of those in the plasma were 4.1 nM (n = 4) and 1.7 nM (n = 2), respectively. However, IQ and MelQx could not be detected in all normal subjects. These results indicate that uremic patients just before induction of hemodialysis treatment are actually exposed to higher levels of the carcinogenic heterocyclic amines, as compared with normal subjects and uremic patients receiving maintenance hemodialysis treatment.