Modifications in the pharmacokinetics of aminoglycosides have been reported among patients with cystic fibrosis. We obtained suction blister fluid (SBF) to study the tissue diffusion of amikacin in cystic fibrosis in 2 children (a 9-year-old boy and a 7-year-old girl) over the course of bronchopulmonary infection. Amikacin was administered intravenously using a single dose of 5 mg/kg. The peak plasma concentrations were 24.5 and 11.2 mg/l, and the peak SBF concentrations were 8.3 and 3.2 mg/l. The ratio of the area under the curve in SBF and plasma was 58 and 60%, respectively. These results suggest a good penetration of amikacin through SBF and a good tissue diffusion of amikacin. The preliminary data suggest that the suction blister method may be useful to assess the tissue diffusion of drugs.