The aim of the studies was to determine the stability of metronidazole using UV spectrophotometric method in 0.5% w/w eye drops which were prepared under aseptic conditions and thermally sterilized. 0.9% solution of NaCl, 5% glucose and phosphate buffers of pH 6.97 and 6.81 were used as the solvents of metronidazole in the drops. Thiomersal and phenylmercuric borate were used to preserve the drops. The viscosity of the eye drops was increased using the solution of polyvinyl alcohol. The drops were stored in tightly closed glass infusion bottles, protected from light. For the stability of analysis a long-term assay was used under controlled conditions following the requirements of ICH, i.e., the time of storage was 24 months at the constant temperature of 25 +/- 2 degrees C and constant humidity of 60% +/- 2% RH. The eye drops containing metronidazole were significantly physically and chemically stable: after 24 months of storage the metronidazole concentration in the drops was close to 100% of the initial concentration. The drops were colorless and transparent. Physical and chemical properties such as pH, osmotic pressure and viscosity underwent insignificant changes during the storage. The preservation test showed that the degree of reduction of the pharmacopeal strains of micro-organisms in freshly prepared drops and in those stored for 24 months at the temperature of 25 +/- 20 degrees C was in agreement with the requirements of Ph. Eur. 6.