This study investigated the levels of adrenomedullin (AM) and the gene expression of AM, calcitonin receptor-like receptor (CRLR), receptor activity-modifying proteins (RAMPs), and receptor-coupling protein (RCP) in the testis, ventral prostate, seminal vesicle, and epididymis in rats aged 3, 12, and 20 months by radioimmunoassay and semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). The results indicate an age-related increase in AM and its messenger RNA (mRNA) levels in the testis and decrease in the sex accessory glands. The gene expression of CRLR and RCP decreased only in the sex accessory glands. The changes in the gene expression of RAMPs suggest that the major increase was in CGRP receptors in the testis, whereas the major decreases in the ventral prostate and the seminal vesicles might be CGRP and AM receptors, respectively. The decreases in these receptors were similar in the epididymis. The results suggest possible roles of AM in the male reproductive system during aging.