The purpose of the studies was to choose additives for eye drops containing cefazolin and the assessment of the influence of used additives and the storage temperature on the physicochemical properties and the stability of the eye drops. The drops were 1% sterile solutions of cefazolin in citrate buffer of pH 6.15-6.20. The drops were preserved with 0.002% thiomersal or 0.001% phenylmercuric borate mixed with 0.4% beta-phenylethyl alcohol. Viscosity of the eye drops was increased using polyvinyl alcohol (PVAL). The pharmaceutical compatibility test of selected additives with cefazolin showed the pharmaceutical interaction of 1% solution of cefazolin with higher than 0.003% concentration of thiomersal, 0.005% benzalkonium chloride and 0.01% chlorhexidine diacetate. The drops, protected from light, were stored at the temperature of 4 degrees C and 20 degrees C. As the criteria of the qualitative assessment of freshly prepared drops and during their storage, the following properties were considered: organoleptic analysis, sterility, pH, osmotic pressure, density, viscosity, antimicrobial activity of cefazolin and preservation efficiency of thiomersal and phenylmercuric borate in the eye drops. The studies showed that the storage temperature did not influence the physicochemical properties of the drops or the antimicrobial activity of cefazolin in the drops, which was not influenced by the used additives either. After 30 days of storage at both temperatures, cefazolin in the eye drops retained 100% of its initial activity. Phenylmercuric borate, whose antimicrobial activity in the eye drops was compatible with the preservation assay cited in the Polish Pharmacopoeia (PPh V), can be used to preserve the drops containing cefazolin.