(I) Fourteen adult male rabbits have been subjected to unilateral isolation of the tail of the epididymis in the abdomen, with subsequent retention of the organ in an abdominal position. Isolation of the contralateral cauda epididymidis in each rabbit was effected in the scrotum as a control measure. (2) Estimates of the proportion of dead and decapitated spermatozoa as well as the incidence of spermatozoa with coiled tails, at different levels of the tubule distal to the point of isolation, have demonstrated a delayed response of so-called mature spermatozoa to the conditions of experimental cryptorchidism. (3) Quantitative assessments of these criteria have suggested that spermatozoa in the body of the epididymis are more susceptible to degeneration than those in the tail of the epididymis, but it is pointed out that more evidence is yet required on this matter. (4) The overall results are discussed in relation to previous work concerning the origin of similar sperm abnormalities.