The urinary excretion of the DNA alkylation products 3-methyladenine (3-MeAde) and 3-ethyladenine (3-EtAde) after controlled exposure to cigarette smoke over a period of 4 days was determined by competitive radioimmunoassay after separation by HPLC. Twenty-four hour urine samples were collected from five smokers and five non-smokers. Days 1 and 3 (control days) were without smoking, on days 2 and 4 smokers consumed 24 cigarettes each within 8 h in an unventilated room (45 m3) in the presence of non-smokers. Average levels of carbon monoxide during exposure were 15-20 p.p.m., 2.8-3.5 mg/m3 of respirable suspended particles and 75-86 micrograms/m3 of nicotine. Carboxyhemoglobin levels increased by 9.0 and 1.8% in smokers and passive smokers respectively. On control days, urinary excretion of 3-MeAde was similar in smokers and non-smokers (4.7-6.2 micrograms/24 h). Smoking resulted in a significant increase (P < 0.01) in 3-MeAde excretion (13.6-14.8 micrograms/24 h); no change was observed in the average excretion of 3-MeAde by passive smokers (4.8-4.9 micrograms of 3-MeAde/24h). Baseline 3-EtAde excretion on control days was similar in smokers and passive smokers (13.7-32.8 ng/24 h). In smokers, the amount of urinary 3-EtAde was increased > 5-fold (119.3-138.5 ng/24 h) on smoking days; no effect on 3-EtAde excretion was observed on average in passive smokers (18.0-25.2 ng/24 h). The nature of the DNA-reactive agent(s) responsible for the increased urinary excretion of 3-alkyladenines, in particular of the sensitive indicator 3-EtAde, remains to be determined.

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