An oral combination of piperazine and ivermectin was used over a 6-week period for treating three different colonies of mice or rats infested with Syphacia obvelata, Syphacia muris or Aspiculuris tetraptera. No acute toxic effect was found in transgenic lines of mice or rats with these products in a preliminary trial. The colonies were treated with piperazine, 2.1 mg/ml in tap water for 2 weeks, then with ivermectin, 0.007 mg/ml, in tap water for the third and fourth weeks, and finally with piperazine for two further weeks. Hygiene measures such as a complete cage change, thorough disinfection and cleaning of the rooms were associated with the treatment. All examinations subsequent to completion of treatment have proved negative for further parasites.