Fosfomycin induces uptake of [3H]tobramycin (2.3 μg/ml) in P. aeruginosa ATCC 27853 in a dose-dependent fashion. Incorporation of [3H]tobramycin into bacterial cells was determined 5 min after addition of unlabeled fosfomycin (0, 0.05, 0.1, 1, 10, or 100 μg/ml). Values represent the means ± SD from four independent experiments. Statistical differences were evaluated by Student's t test (*, P < 0.05; **, P < 0.005).