Treatment of strongyloidiasis has been traditionally based on thiabendazole, despite its frequent gastrointestinal side effects and failure to achieve eradication of the parasite from faeces in approximately 30% of cases. Ivermectin has been shown to be more effective for treating chronic uncomplicated strongyloidiasis. The efficacy and tolerability of these drugs in a series of patients treated from 1999 to 2002 at the Oliva Health Centre, Valencia, Spain, are reported. A total of 88 patients diagnosed of strongyloidiasis were treated using the following regimens: thiabendazole 25 mg/kg/12 h for 3 consecutive days in 31 patients; ivermectin 200 mug/kg as a single dose in 22 patients; and ivermectin 200 mug/kg for 2 consecutive days in 35 patients. The efficacy and side effects were recorded. A total of 65 patients were male, and 23 female. The mean age was 64 +/- 12 years. Of the patients, 44 had worked barefoot in rice fields. Among the 31 patients treated with thiabendazole, 25 (78%) met the criteria for cure (the absence of parasite in faeces after examination of three samples collected on alternate days), and 5 (16%) experienced side effects (asthenia, epigastralgia and disorientation). Of the 22 patients treated with ivermectin on a single day, 17 (77%) met the criteria for cure, and 2 (9%) reported side effects (dizziness, dyspepsia). Among the 35 patients treated with ivermectin on 2 consecutive days, 100% met the criteria for cure, and 0% experienced side effects. In chronic uncomplicated strongyloidiasis, a treatment regimen consisting of ivermectin 200 mug/kg for 2 consecutive days provided the best results with regard to efficacy and tolerability. When the eosinophilia continued after treatment, we observed a high percentage of not-cure rate (7 of 9 patients, 77%).