Eggs from the pig roundworm Ascaris suum are easily obtainable in large numbers from uterus of adult worms. It is therefore natural that eggs isolated from that organ have been used almost exclusively in experimental ascariasis, both in the natural host (Kelley & Nayak 1965, Gaafar & Keittevuti 1972, Andersen et al. 1973, Jørgensen et al. 1975 and others) and in small laboratory animals (Jeska et al. 1969, Berger 1971 and others). In some cases no details are given on the origin and preparation of the infective eggs or the eggs may originate both from uteri of adult worms and from pig faeces (Kelley et al. 1957).