Two strains of clostridia, isolated from the rumen fluid of sheep as potential antagonists toward anaerobic fungi showed a complete array of chitinolytic enzymes. Enzyme tests in cultures demonstrated endochitinase, exochitinase, N-acetyl-glucosaminidase, chitosanase and chitin deacetylase activities mainly in the extracellular fractions. In all samples, the highest was the activity of exochitinase (600-1100 nmol mL-1 h-1); the activity of endochitinase (280-500 nmol mL-1 h-1) was also significant. Chitinases were stimulated in the presence of reducing compounds and no dependence on cations was observed. In both strains different isoforms of chitinases of molar mass 36-96 kDa were detected. The chitinases from our isolates lyzed cell walls of anaerobic fungi in vitro and inhibited the activity of fungal beta-1,4-endoglucanases. Of the two bacteria examined, one was more effective in both antifungal effects.