The specific aim of this study was to compare the frequency of sister chromatid exchange (SCE) in peripheral lymphocytes using it as a biomarker of integral exposures to carcinogens in 14 untreated newly-diagnosed nasopharyngeal carcinoma (NPC) patients, 16 untreated newly-diagnosed cervical cancer patients, and 30 healthy controls matched with patients on age, sex, cigarette smoking and alcohol drinking. Peripheral lymphocytes were cultured in RPMI 1640 medium containing 20% fetal calf serum and 6 microM phytohemagglutinin. After culture for 24 hours, 20 microM 5-bromo-2-deoxyuridine was added into the medium. Colcemid solution was further added after 70 hours. Harvested cells were stained with Hoesch 33258, illuminated, and restained with Giemsa. The SCE frequency was scored by two readers independently and blindly. The results showed a significantly increased SCE frequency in lymphocytes for NPC patients (mean +/- standard error = 14.7 +/- 1.7 SCEs/cell) compared with their matched controls (10.1 +/- 0.7 SCEs/cell) and for cervical cancer patients (12.0 +/- 0.9 SCEs/cell) compared with their matched controls (9.2 +/- 0.7 SCEs/cell). These results suggest that NPC and cervical cancer patients have a higher integral exposures to both viral and chemical carcinogens than matched controls.