The pharmacokinetics of amikacin after intravenous (IV) and intrapleural injection was compared in 25 patients with pleural drainage after lung resection. In ten patients 7.5 mg/kg of the drug was injected IV; the mean peak concentrations were 31.2 +/- 2.3 micrograms/ml in the serum and 13.3 +/- 3.8 micrograms/ml in the pleural fluid. The penetration of amikacin in the pleural space was 80 percent. After the intrapleural injection of the same dose of amikacin in 15 patients, the pleural fluid concentrations of the drug were extremely high and well sustained during eight hours; however, serum concentrations reached maximal values of 14.1 +/- 4.7 micrograms/ml, indicating a substantial diffusion of amikacin from the pleural space to the blood. In the case of treatment of pleural infections by local injection of aminoglycosides, the serum concentrations must be kept in mind to avoid systemic intoxication from these drugs.