Investigations on parasitic infestations in laboratory animal stocks under different keeping conditions were carried out by fecal sample examination. Only barrier-kept mice and rats proved to be free of infections. Under semi-open or conventionally keeping conditions mice were infected with Aspiculuris tetraptera and Syphacia obvelata (max. 94.7 + 69.7%), rats with A. tetraptera and S. muris (48.6 + 94.9%), and hamsters and mongolian jirds with S. obvelata (26.6 and 16%, respectively). Ivermectin, added to the drinking water for the elimination of murine oxyurids, over a 24-hour period, in a dosage of 1.0 (males) and 1.6 mg/kg body weight (females), proved to be highly effective against A. tetraptera; the treatment of S. obvelata-infections requires a dosage correction.