This study was an examination of the dose response of the kinematics of human sperm motion to 1-min and 30-min incubations with the spermicide Nonoxynol-9 (N9). At concentrations resulting in only slight reductions in percentages of motile sperm (MOT), increasing N9 decreased the progressiveness of sperm motion (reflected in decreasing straight line velocity). This decline in progressiveness resulted from both decline in the vigor (reflected in decreasing curvilinear velocity; VCL) and disruption of the pattern (reflected in decreasing linearity; LIN) of such motion. Since, after the 1-min incubation, VCL declined only slightly for seminal sperm over this range of N9 concentrations, declines in sperm progressiveness were primarily due to decreases in LIN. For sperm collected from the pellet fraction from a Percoll gradient technique, however, VCL declined substantially even at low concentrations of spermicide. These Percoll-separated sperm were, on the other hand, less sensitive to N9 than seminal sperm in terms of the dose response of MOT. This added resistance may be attributed to selection or to environmental or physiological changes caused by Percoll separation. Responses in mean amplitude of lateral head displacement (ALH) to increasing N9 also differed for the two treatments, increasing on average for seminal sperm while decreasing on average for Percoll-separated sperm.