Techniques for assessing rat sperm motility utilizing computer assisted semen analysis (CASA) systems were discussed. The features of CASA systems were described. CASA systems typically consist of a microscope, stage warmer, video cassette recorder, and a computer. A CASA analysis of sperm motion was based on the system receiving a constant illumination from the sperm head because of its greater volume relative to the midpiece and tail. Analysis of human sperm motion by a CASA system was relatively easy. Analysis of rat sperm motility was more difficult because of the flattened hook shape of the sperm head. Because of this, the apparent shape of the head as determined by the instrument appeared to be constantly changing, making it difficult to follow the instantaneous motion of the head. Developing CASA techniques for studying rat sperm motility has been slower than for other species that have more symmetric heads such as primates and ruminants. This has resulted in laboratories utilizing different methods for collecting rat sperm motility data, which are difficult to interpret. The results of a consensus of CASA system users for optimizing collection of rat sperm motility data were discussed. Topics covered included the effects of euthanasia techniques, semen sampling site, sample collection method, type of buffer used to dilute the samples, chamber configuration, and operational settings of the CASA system.