Human cervical mucus from women using Lippes Loop and T-Cu-200 IUDs was used to study sperm migration in vitro using flat capillary tubes. Cervical mucus from women bearing no IUD was used as the control. 100% of the control samples, 83% of the Lippes Loop users, and 88% of the T-Cu-200 users had more than 100 spermatozoa/field of 100x. In 17% and in 11% there were between 40 and 100 spermatozoa/field of 100x in the Lippes Loop and T-Cu-200 users. The presence of copper IUDs does not interfere with sperm migration in vitro through human cervical mucus.