The types and averages of abnormal sperm were studied in the epididymis of adult and aged golden hamsters. Abnormal spermatozoa represent 14.6-19.6% of the total of spermatozoa in adults, 31.7-42.1% in middled-aged hamsters, and 39.3-50% in advanced-aged hamsters. Twelve abnormal shapes were found, with the lack of an acrosome, the lack of a head, and the coiling of the tail, being the most frequent in the three age groups. An important increase in the number of coiled spermatozoa was found in the corpus and proximal cauda of the epididymis, but a decrease was observed in the distal cauda. Our data suggest that the epididymis produces secondary defects in spermatozoa running from the proximal caput to the middle zone of the duct, but that many of these spermatozoa are eliminated in the distal cauda. Such a result is mainly found in aged animals, in which a higher percentage of abnormal sperm from secondary origin is found with respect to adults.