A method was developed for the isolation of viable cells from rat lungs. The cells were a heterogeneous population, which maintained a high percentage viability for up to 3 hr on incubation at 37 degrees. Reduced cofactor levels (NADH, NADPH) decreased on incubation, but ATP remained constant. The cells were active in the metabolism of the two xenobiotics studied. A model compound, 7-ethoxycoumarin, was O-deethylated and subsequently conjugated with glucuronic acid and sulphate, whilst a pharmaceutical agent, N-acetylcysteine, was de-acetylated.