In this study, the pH-rise during storage of extended porcine semen was examined. This pH-rise was found to be caused by CO(2)-loss from the buffering system in the extender and was more pronounced with increasing air volume in the recipient. An influence on sperm motility parameters was observed between semen samples stored in the presence of different amounts of ambient air in the recipient. Velocity parameters and percentage motile spermatozoa were significantly lower for semen stored in recipients with higher air volume and elevated pH. Adjusting extender preparation by avoiding air contact in commercial AI-centres may minimize the pH-rise and its influence on sperm motility.