Many macropodids exhibit lactational quiescence during which an embryo produced at post-partum mating is retained as a blastocyst in utero while a pouch young is sucking. The sucking stimulus maintains secretion of prolactin which may in some species inhibit the activity of the corpus luteum and, hence, the development of the embryo. When the sucking frequency decreases, the blastocyst resumes development. In the present study, the dopamine agonist bromocriptine, which in many mammals results in decreased secretion of prolactin from the pituitary gland, was administered to the Tasmanian bettong (Bettongia gaimardi) at two different doses (12.5 mg kg(-1) and 5 mg kg(-1)). Although lactation was affected by both doses, as evidenced by slower growth of the pouch young or their loss, in only two cases did the quiescent blastocyst activate at the time of injection. This occurred with the highest dose of bromocriptine and was reflected by earlier changes in plasma progesterone concentrations. It is concluded that the Tasmanian bettong is unusual in its lack of sensitivity to bromocriptine.