1. The modified critical test, or so-called short-term slaughter test, was the most suitable means of assessing anthelmintic efficacy on adult Trichostrongylus spp. and O. columbianum. It has some value for O. circumcincta but is unsatisfactory on H. contortus.
2. The modified controlled test was the best method of testing the effects of anthelmintics on immature worms. It is the method of choice on all stages of development of H. contortus.