OBJECTIVE: To investigate whether semen parameters in infertile couples who undergone intrauterine insemination (IUI) change in the subsequent IUI cycle and the subsequent in vitro fertilization (IVF) cycle. METHODS: Fifty-three infertile couples who had failed to become pregnant after the first IUI cycle with computer-assisted semen analysis (CASA) were included. After the first IUI, thirty-eight couples underwent the second IUI (Group 1), and fifteen underwent IVF-ET procedure (Group 2). All semen parameters including semen volume, concentration, motility and total motile sperm count were analyzed in the second IUI or IVF-ET procedure for comparison with the result of first IUI. RESULTS: There were no significant differences in husband age, interval between the first and second procedure and cause of infertility. In Group 1, only sperm motility at the time of the latter IUI was significantly decreased when compared to the former IUI irrespective of the first semen parameters. In Group 2, sperm concentration, motility and total motile sperm count at the time of subsequent IVF were lower than the former IUI. By sub-analyses of Group 2, in the group of optimal semen parameter at IUI cycle, sperm concentration and total motile sperm count at the time of subsequent IVF were lower than the former IUI, while in the group of suboptimal semen parameter at IUI cycle, only sperm motility at the time of subsequent IVF were lower than the former IUI. CONCLUSION: The semen parameters in couples converted to IVF cycle were more adversely affected than those remained in IUI cycle. Further study on psychological stress should be necessary to explain the reason.