In the female tammar wallaby, Macropus eugenii, which has a highly seasonal breeding pattern, teat eversion and enlargement of the pouch occur at puberty, about 40 weeks after birth. The most obvious sign of puberty is teat eversion: 22 of 23 wild caught, and 23 of 24 captive postpubertal animals had fully everted or everting teats. Full eversion of the teats took on average two to three weeks after puberty. The pouch opening enlarged at puberty, and the rate of enlargement from 2 weeks before puberty to 2 weeks after puberty was significantly greater than the rate before puberty. In a group of pouch young ovariectomized at 5-10 weeks of age, no such changes in either teats or pouch were observed by 46 weeks of age. However, after treatment with oestradiol (0.5 microgram kg-1 body mass), four of five young showed teat eversion within 3-4 weeks. Progesterone (2 mg kg-1) had no effect on inverted teats. In these ovariectomized females oestradiol treatment caused a significant increase in the rate of growth of the pouch opening. During progesterone injections the size of the pouch remained the same. Thus, at puberty the teats and pouch of the tammar wallaby undergo rapid developmental changes and growth. Ovariectomy at an early stage of gonadal differentiation disrupts these normal changes, but treatment of these animals with physiological doses of oestradiol at the age when puberty would normally have occurred can restore teat and pouch maturation. Teat eversion and pouch enlargement can therefore be used as markers for puberty.(ABSTRACT TRUNCATED AT 250 WORDS)