Summary. Rabbit antibody to human cervical mucus was used in the immuno-electrophoretic analysis of cervical mucus, seminal plasma and blood serum. Eleven antigens were found in cervical mucus, but no more than nine in any one sample. One post-coital sample of cervical mucus in the pool used to produce the antiserum contained an antigen, thought to be prostatic acid phosphatase, derived from the semen contamination. Three antigens appeared specific for cervical mucus, being absent from seminal plasma and serum. Another two antigens were shared with seminal plasma and serum, two were shared with seminal plasma only, and a further two were shared with serum only.Two of the cervical mucus antigens were identified as immunoglobulin-G and albumin, and another two were believed to be transferrin and \g=a\-1 antitrypsin.