In this study, concentrations of amikacin in blood and bronchial secretions of 10 patients with mechanical ventilation for acute respiratory failure due to pneumonia were measured. One-half of the patients received amikacin twice daily, and the others received once-daily administration. Concentrations in bronchial secretions of the patients treated twice daily ranged from 3 to 4 mg/liter, i.e., they were similar to those in previously published reports. Peak concentrations in bronchial secretions occurred between 3 and 4 h after the onset of infusion, and they reached 4.8 +/- 2.6 mg/liter on day 1 and 4.0 +/- 2.7 mg/liter on day 3. For the patients treated with amikacin once daily, concentrations in bronchial secretions were more than twofold higher, above 8 mg/liter for 12 h. Peak concentrations in bronchial secretions occurred between 3 and 4 h after the onset of infusion and reached 13.6 +/- 9.3 mg/liter on day 1 and 10.4 +/- 3.5 mg/liter on day 3. These concentrations are higher than the MICs for less sensitive bacterial strains, such as Acinetobacter spp. and Pseudomonas aeruginosa.