Abstract An experiment was designed to develop an objective technique for measuring rooster sperm motility. A Beckman Spectronic 20 spectrophotometer was used to measure optical densities of sperm suspensions while they were flowing through the spectrophotometer. A motility index (MI) based on the decrease in optical density after the flow was stopped was calculated. The MI was found to be highly significantly correlated (P It was also found that the MI was not more variable than the percent motility or the vigor. There were no correlations between the three motility measurements and fertility. It was concluded that the technique provides a rapid and totally objective measure of the motility of rooster sperm.