In vivo studies in male nude rats bearing tumors bilaterally,a P-gp-negative small cell lung carcinoma (GLC4) and its P-gp-overexpressingsubline (GLC4/P-gp) showed a 159% higher level of [2-acetyl-11C]daunorubicin in GLC4 than in GLC4/P-gp tumors. The gene discussed is PGP; the disease is small cell lung carcinoma.