Banihani SA, et al. - This study was intended to assess the impact of caffeine at 1, 5, 10, and 20 mm on the motility of human spermatozoa in normozoospermic and asthenozoospermic semen samples, level of seminal nitric oxide, chelation of seminal calcium ions, and activity of seminal creatine kinase. Researchers included 51 normozoospermic and ten asthenozoospermic semen samples. They assessed sperm motility by Makler counter, and seminal nitric oxide, seminal‐free calcium, and activity of seminal creatine kinase were evaluated spectrophotometrically. Thie results of this study exhibited that the progressive motility of human spermatozoa was found to be higher in the presence of caffeine at 10 mM in normozoospermic and asthenozoospermic semen samples; this increase, albeit partially, could be due to elevated activity of seminal creatine kinase, but not to elevated production of nitric oxide or chelation of free calcium ions.