High-affinity and low-capacity molecules that bind 5.alpha.-dihydrotestosterone and estradiol-17.beta. were demonstrated in the canine epididymis. The molecules were proteinaceous in nature, thermolabile and sedimented in a sucrose density gradient with a coefficient of 8S with respect to bovine serum albumin. Only minor differences were found for Kd for estradiol-17.beta. (3.5 .+-. 2.74 .times. 10-10 M) and 5.alpha.-dihydrotestosterone (4.2 .+-. 10.75 .times. 10-10 M) (means .+-. SD) in the 3 anatomically distinct regions of the epididymis.