Orel's kangaroo rat (Dipodomys ordii) was studied to determine age and seasonal variation in reproduction and the relationship between reproduction and environmental parameters. The 423 specimens collected in central Oklahoma during the 13-month study were classified into three age groups based upon cranial characters. Testes 6.8 mm or longer and weighing 0.07 g or more had mature spermatozoa. Adult males were reproductively capable throughout the year. Peak breeding periods in adult females occurred in January through March and in September. The average number of embryos per pregnant female was 2.8. There was a significant correlation (r = 0.681) between the number of corpora lutea and the greatest daily precipitation during the month.