The penetration of minocycline into lung tissue was evaluated in 14 patients about to undergo excision of the lung for cancer. The patients received minocycline orally in doses of 100 mg twice a day for 3 days, the 100 mg in the morning of the operation day. Minocycline concentrations were measured in plasma samples taken before surgery and in the lung tissue resected. The mean tissue/plasma concentration ration was 3.17 +/- 0.41 (range: 1.5 to 7.48). The same ratios were obtained in peritumoral and tumoral tissues. These results indicate that minocycline penetrates well into tissues.