The metabolism of antipyrine (10 mg/kg i.v.) was studied in nine patients with cancer of the lung and in a cancer-free control group matched for age, sex, drug intake, and smoking and drinking history. The mean plasma clearance of antipyrine was 0.0475 +/- 0.009 liter/kg/hr in the tumor group and 0.0557 +/- 0.007 liter/kg/hr in the control group (p greater than 0.05). The antipyrine plasma elimination half-life was longer in the group with tumors (9.5 +/- 1.3 hr) compared to the control group (7.7 +/- 1.3 hr), but the difference was not statistically significant (p greater than 0.05). There was no difference between the groups in the excretion of two major antipyrine metabolites, 4-hydroxyantipyrine and N-demethylantipyrine, in a 48-hr urine sample. Thus, the presence of lung cancer in humans does not significantly alter antipyrine elimination.