Intrauterine insemination (IUI) may lead to very painful uterine cramps, which are due to the effect of the prostaglandin (PG) content of human semen. The purpose of this study is to present the reactivity of the human uterus to the placement of raw semen in the intrauterine space and to evaluate the related response patterns. A statistically significant uterine activity change was observed between the periods before and after intrauterine insemination. Three minutes after IUI, an increase in uterine activity was observed; it became most prominent at five to ten minutes. This stimulation was sustained for 30 minutes and decreased gradually. Although there is an increase in uterine activity following intrauterine insemination, neither pelvic pain nor abdominal discomfort was reported. According to this observation, we suggest that a semen volume of 1 mL might be used safely for intrauterine insemination.