To determine the onset of puberty in Arabian oryx (Oryx leucoryx), a longitudinal study was conducted in 5 captive males at the National Wildlife Research Centre, Taif (Saudi Arabia). From birth to 20 months of age, twice weekly, animals were weighed and blood was assayed for LH and testosterone. Four periods were defined by analysis of the hormonal profile. During the first 5 months (corresponding to prepuberty), mean LH concentrations increased significantly while testosterone remained basal. Testosterone increased significantly during the second period (from 6 to 7 months) while LH decreased significantly. The testosterone pattern suggests that the animals reached puberty at around 7 months old. Mean LH concentrations remained at a similar level before and after puberty and increased significantly between the 12th and 13th months of life. This increment correspond to the transition between two further periods. The third period (8-12 months) was characterized by testosterone peaks of 2.4 +/- 0.1 ng ml-1 which irregularly occurred over a period of 26.6 +/- 2.7 days and was followed by a fourth period, during which peaks were seen at 24.1 +/- 1.6-day intervals and reached 4.7 +/- 0.2 ng ml-1. This last period probably corresponds to the mature stage of puberty. The testosterone cyclicity in oryx, coinciding with the estrous cycle length of the female, would permit the male to be fertile throughout the year and could be an adaptive response to the opportunistic and aseasonal reproductive cycle of the female.