A survey of intestinal parasite infections in school-children throughout Serbia revealed an area of endemic infection where 31% of the children examined were found to be infected with Giardia lamblia, Enterobius vermicularis, Ascaris lumbricoides and Trichuris trichiura. All infected children were treated with metronidazole for giardiasis and mebendazole for helminthic infections. A post-chemotherapy survey was performed 3 months later to assess the efficacy of treatment, showing a decrease in the prevalence of all species, thus indicating drug efficacy of 66-100%. A second survey, performed 13 months after chemotherapy to assess the rates of reinfection, showed that only Ascaris lumbricoides prevalence returned to the pre-treatment level. The results of this field study prove chemotherapy to be an important tool in the control of intestinal parasite infections.