A child with infant botulism became apneic and died while receiving ampicillin and gentamicin therapy. As aminoglycosides have been implicated in the induction and/or exacerbation of neuromuscular blockade, we used an animal model to test the hypothesis that aminoglycosides potentiate neuromuscular blockade of botulinum toxin. In the range of aminoglycoside doses utilized in these experiments, both gentamicin and tobramycin enhance neuromuscular impairment and death of botulinum toxin-exposed mice. These results support recently published clinical observations that aminoglycosides may potentiate neuromuscular weakness caused by botulinum toxin, and suggest that these antibiotics should be used with caution in suspected cases of infant botulism.