The present study reports on attempts to delay puberty in a model marsupial species using the gonadotrophin-releasing hormone (GnRH) agonist deslorelin. Female tammar wallaby pouch young received deslorelin (5 mg) or placebo implants (n=8/group) when they were 193±2 days old. Sexual maturity was significantly delayed in deslorelin-treated animals, with the first successful production of offspring in treated and control animals occurring at 813±62 and 430±42 days of age, respectively. This delay was associated with a period of retarded pouch and teat development. Progesterone concentrations remained at basal levels throughout the first breeding season, indicating the absence of luteal cycles in treated females. Recovery and maturation of the hypothalamic-pituitary axis was a gradual process. Treated animals failed to respond to GnRH challenge at 12 months of age and had a reduced LH response at 18 months of age, before attaining full responsiveness by 24 months of age. Despite this apparent pituitary recovery by 24 months of age, as evidenced by complete teat eversion and LH responsiveness to GnRH, the time to first parturition was significantly delayed beyond this time in three females. This suggests that there may be longer-lasting effects at the level of the ovary and/or on FSH secretion. The significant delay in the onset of sexual maturation in response to chronic GnRH agonist treatment in this model marsupial species may be of practical significance to the management of fertility in captive and semi-free range marsupial populations.