Hyperactivation and acrosome reaction are prerequisite steps for sperm to be able to fertilize an oocyte. In mammals, hyperactivation is defined as a movement pattern seen in spermatozoa at the site and time of fertilization. The objectives of the present experiments were to analyze the process of hyperactivation and to investigate its relationship with progesterone evoked intracellular calcium concentration ([Ca2+]i) increase and their implications with infertility. After capacitation the sperm from patients, when compared with donor's sperm, showed decreased percentage of hyperactivated sperm, molitily, progressive motility, and curvilinear velocity (VCL). On the other hand, the linearity (LIN) was increased. Amplitude of lateral head displacement (ALH) and [Ca2+]i increase (peak and plateau from baseline) showed good correlation in patients with infertility. These data suggest that impaired hyperactivation might be involved in the pathophysiology of infertility.