In this study a comparison between two different methods for measuring the susceptibility of Giardia lamblia trophozoites to metronidazole and albendazole is performed. Modifications of Meloni's method, based on the loss of adherence of parasites to surfaces, and the Hill method, based on the loss of parasite division capacity, are compared. A logistic model was used to calculate the inhibitory concentrations IC(10), IC(50) and IC(90) that were further compared using the respective standard errors. The results obtained, after contact of parasites with the antiparasitic drugs for 24h, show that the adherence method is more sensitive than the multiplication method for low and moderate inhibitory concentrations of albendazole. Conversely for metronidazole the multiplication method seems to be more sensitive for high inhibitory concentrations of the drug. For screening the IC(50), both methods seem to be effective, however, the inhibition of adherence method have even better performance for the benzimidazole like drugs.