Background: The effect of storage temperature and time on blood gas and acid-base values has been investigated intensively in cattle and dogs; however, data are lacking in other species. Objective: The aim of our study was to evaluate changes in gas composition and acid-base values in venous blood stored at different temperatures and for different times in 4 domestic species in Italy. Methods: Blood samples from Comisana sheep (n=10), Maltese goats (n=10), Ragusana donkeys (n=10), and Thoroughbred horses (n=10) were analyzed after storage at 23°C (room temperature) for 15 minutes (group I), 23°C for 1 hour (group II), 37°C for 8 hours (group III), and 4°C for 24 hours (group IV). Results were analyzed using a 1-way repeated measures ANOVA. Results: In all species no statistically significant differences in pH values were present in samples stored at 4°C for 24 hours. This also was true for Pco2 in all species except the horse. Except for HCO3− concentration in the horse, significant changes in Po2, HCO3− concentration, base excess, and the standard bicarbonate concentration were observed for all species in samples stored at 4°C. In samples stored for only 1 hour at room temperature, significant changes in most analytes were detected. Conclusions: The results of this study underline the need for rapid assessment of acid-base samples, because any delay, even for 1 hour, may affect the results.