The combined effect of the Lymphatic Filariasis Elimination Programme (LFEP) and the National Schistosomiasis and Soil-transmitted Helminthiasis Control Programme (NSSCP) on soil-transmitted helminthiasis (STH) was evaluated. In September 2004, before mass drug administration (MDA) with ivermectin and albendazole by the LFEP in October, the prevalence and intensity of STH were recorded in 228 pupils in one primary school. After 8 months, all available pupils were re-examined, and the prevalence of Ascaris lumbricoides, Trichuris trichiura and hookworm had decreased from 0.9 to 0.7% (P=0.84), from 4.8 to 0.7% (P=0.004) and from 45.6 to 11.9% (P<0.001), respectively. Overall, 81.2% of the schoolchildren stated that they were treated by the LFEP in October 2004. After the 8 months follow-up, pupils were treated with praziquantel and albendazole by the present project (substitute for the NSSCP). After another 4 months (at 12 months follow-up), the prevalence of hookworm infection was reduced to 4.8% (P=0.003), while the prevalence of T. trichiura was reduced to 0.3% (P=0.54) and the prevalence of A. lumbricoides remained unchanged. Mass co-administration of ivermectin and albendazole by the LFEP had a significant effect on STH, which was further amplified by treatment with praziquantel and albendazole 4 months later.