A prospective, randomised, open study compared a 7-day course of oral albendazole 800 mg daily with a single oral dose of the parenteral veterinary preparation of ivermectin in 42 Thai patients with chronic strongyloidiasis (21 in each group). The primary endpoints were relief of symptoms (if present) and clearance of Strongyloides larvae from faeces immediately after treatment and at follow-up to 16 weeks later. Cure rates in the albendazole and ivermectin groups were 38.1% and 76.2%, respectively, (P=0.029) in the intention-to-treat analysis and 50% and 88.9%, respectively, (P=0.023) in the per-protocol analysis. Acute generalised exanthematous pustulosis developed in one patient who was treated with the veterinary preparation of ivermectin. This study confirms the superiority of ivermectin compared with albendazole as well as that oral use of the parenteral veterinary preparation in humans is as effective and safe as human preparations.