Metronidazole was given to rats with experimentally induced inflammation to evaluate whether the drug has any antiinflammatory effect. Inflammation was caused by injection of Freund's complete adjuvant into a paw. The oedema of the paw measured on the 4th day was not influenced after metronidazole 20 mg/kg/day or 160 mg/kg/day, whereas phenylbutazone 80 mg/kg/day significantly decreased the volume of the paw. The concentration of orosomucoid did not differ in the group of rats given metronidazole 20 mg/kg/day as compared to the control group. However, the orosomucoid concentration was lower in the group given metronidazole 160 mg/kg/day, as was the case in the phenylbutazone group. In groups of rats with polyarthritis studied on the 14th and 21st day there was no difference of arthritic index, volume of paw or orosomucoid concentration in neither low nor high dose metronidazole as compared to the control groups. The phenylbutazone groups, however, showed a lower arthritic index, lower volume of paw and lower orosomucoid concentration.