Cell‐mediated immune response to washed, frozen and thawed mouse epididymal sperm after experimental vasectomy has been studied in vitro. Vasectomy without vasoligation results in cellular sensitization to sperm‐specific antigens. This is in contrast to conventional vasectomy where this does not occur. It is believed that the detected cellular response may be due to extravasation of spermatozoa. However, neither the antigen(s) responsible nor the mechanism(s) involved are clear.