The purpose of the studies was to examine the influence of additives and the storage temperature on the physicochemical properties of the eye drops containing ceftazidime and on the antimicrobial activity of ceftazidime in the eye drops stored for 30 days at the temperature of 4 degrees C and 2 degrees C. The eye drops were 1% sterile aqueous solutions of Biotum (Ceftazidimum) in citrate buffer of pH 6.18-6.30, which were preserved with 0.002% thiomersal or 0.001% phenylmercuric borate mixed with 0.4% beta-phenylethyl alcohol. The viscosity of the eye drops was increased with polyvinyl alcohol. The pharmaceutical compatibility test showed the pharmaceutical interaction of 1% solution of Biotum with thiomersal at the concentration higher than 0.003%, with 0.01% chlorhexidine diacetate and with 15% polyvinylpyrrolidone. As the criteria of the qualitative assessment of both freshly prepared eye drops and those stored at the temperature of 4 degrees C and 20 degrees C, the following analyses were considered: organoleptic analysis (color, clarity, and smell), sterility, pH, osmotic pressure and viscosity. The antimicrobial activity of ceftazidime and the preservation efficiency of thiomersal and phenylmercuric borate in the eye drops were determined using methods of the Polish Pharmacopoeia VI (PPh VI). The antimicrobial activity of ceftazidime in the drops was especially influenced by their storage temperature. After 30 days of storage at the temperature of 4 degrees C, there was no decrease of antimicrobial activity of ceftazidime detected in the eye drops. However, when the eye drops were stored at the temperature of 20 degrees C, the decrease of antimicrobial activity of ceftazidime was observed already after 14 days. After 30 days of storage both at the temperature of 4 degrees C and 20 degrees C, neither pH nor viscosity of the eye drops changed; however, the osmotic pressure was decreased.