During 2004-2007 the efficacy of benzimidazole type drugs was studied on 14 sheep farms in the Czech Republic. The study was based on the evaluation of faecal egg count reduction test (FECRT), egg hatch test (EHT), and larval development test (LDT). The prevalence of benzimidazole resistance on farms ranged from 25% to 98%; however, the infection intensity was typically low to moderate on most of the farms. Based of FECRT, resistance was identified on three farms. Resistance was suspected on one of the farms after repeated examination performed the following year.