Seasonal variation in serum testosterone, thyroxin and the testicular morphology were studied in 54 sexually mature and apparently healthy one-humped camels during the different seasons of the year. The testosterone and thyroxin serum levels were measured and 3b-hydroxysteroid dehydrogenase activity of Leydig cells was assessed immunohistochemically to aid in the interpretation of results. The activity of 3b-HSD was high during cold months and severely depressed to the minimum activity in hot months. Concomitantly, serum testosterone and thyroxin levels increased during the winter and early spring and decreased thereafter. Their levels reached the peak during the months of January till April. These results suggested that 3b-HSD is a key enzyme in the regulation of the testosterone production in Leydig cells of the male dromedary. Thyroxin is a crucial hormone for the male reproductive activity during the breeding season in the dromedary and fluctuated in the same pattern as serum male androgen.