This study compares functional parameters of sperm from ejaculates collected from 15 adult male chimpanzees using rectal probe electrostimulation (RPE) and from 10 adult male chimpanzees trained to use an artificial vagina (AV). Computer assisted motion analysis (CAMA) showed no significant differences in mean values for straight line velocity (VSL), linearity (LIN), curvilinear velocity (VCL), and lateral head movement (ALH) of sperm from ejaculates collected by RPE and by AV. There was, however, a significant difference (P < 0.01) in the population distribution for VSL and LIN, which indicates that sperm swim in a more convoluted manner in ejaculates collected by RPE than in ejaculates collected by AV. In the hamster zona-free ovum penetration assay (SPA), there were no significant differences in the percentages of hamster oocytes penetrated by sperm or in the number of sperm which penetrated each oocyte after 4 or 24 h incubation using sperm from ejaculates collected by RPE and by AV. Therefore, the lack of success using sperm from ejaculates collected by RPE to initiate pregnancy in the chimpanzee does not appear to result from abnormalities in sperm fertilizing capacity as measured in SPA.