Fractional acetylation of plasma sulphadimidine 6 h after dosing with 40 mg/kg metabolically active mass (p.o.) was measured in 53 patients with primary lung carcinoma and in 31 controls. Sixty percent of all tumour patients and 58% of controls were slow acetylators. There was no statistical evidence (P greater than 0.5) of association between acetylator phenotype and lung carcinoma.