The kinetics of degradation of azlocillin sodium in four intravenous admixtures was investigated at different temperatures. The effect of temperature has been determined and from this data, by applying of Arrhenius-law, the stability of azlocillin sodium at 25 degrees C has been predicted and the t90 was determined. Admixtures containing azlocillin sodium (0.01 g ml-1) were prepared in 0.9% sodium chloride injection, in 5% dextrose solution, in 5% levulose solution and in Ringer's lactate solution. The admixtures were stored at 30 degrees, 40 degrees and 50 degrees C in either polyvinyl chloride bags and glass bottles. The change in the initial azlocillin sodium concentration was related to the type of intravenous solution. No dependence with material of container was found. After 24 hours, the change in the initial concentration of penicillin was less than 10% of the initial concentration in 0.9% sodium chloride and 5% levulose solution. However in Ringer's lactate and 5% glucose solution the t90 was lower. These results were found in agreement with experimental ones obtained at room temperature.