Three courses of thiabendazole therapy, including one course given directly into a blind loop of the bowel, failed to eradicate Strongyloides stercoralis from a 55-year-old man who had undergone a Roux-en-Y operation. The patient responded to 1.5 g/day of mebendazole for 14 days, and the infection did not recur. Our case illustrates the difficulty of eliminating S stercoralis from a blind loop of the bowel and indicates that mebendazole therapy used in adequate doses is effective treatment for strongyloidiasis. The lack of toxicity of mebendazole makes it a desirable drug for Strongyloides infestation resistant to thiabendazole therapy.