Plasma concentrations of LH, progesterone and oestradiol were measured in 5 cyclic swamp buffaloes. Progesterone levels began to increase after Day 5 (Day 0 = the day of oestrus) and reached a plateau after Day 10. A rapid decrease in progesterone levels occurred during the 5 days before oestrus, followed by a sustained increase in oestradiol concentrations. Basal LH levels decreased towards the mid-luteal phase and then progressively increased during the follicular phase.