The effects of potassium, sodium, chloride and calcium on the percentage progressive motility of samples of chimpanzee and bull spermatozoa were investigated. Inhibitors and stimulatory of motility were identified. Three parameters of chimpanzee sperm motility, velocity, frequency and amplitude, were measured. There was no consistent change related to ion concentration. The ionic constituents of chimpanzee and bull seminal plasma were also analysed.