The overall prevalence of Chlamydial (past and current) infection as detected by both ELISA and Real-TM PCR in the unexplained infertility group was 40 % (20/50) while the prevalence in the control group was much lower of 18.2 % (all of them being only IgG sero-positive indicating past Chlamydial infection) where none of the controls were positive for IgM Abs or PCR positive. This evidence concerns the gene CD40LG and Infertility.