Most, or all, wild females of Trichosurus vulpecula bred during the first 6 months of the year and some bred again during the second half of the year. In captive females the oestrous cycle varied in length from 22 to 58 days but all cycles longer than 32 days began between 20 April and 16 June. During two periods of each year, from early February until 20 April and from 16 June until late September, the cycle varied in length from 22 to 32 days (mean: 25\m=.\69\m=+-\0\m=.\31 days). The females were polyoestrous and monovular and the gestation period was about 17\m=.\5 days.Vaginal smears from mated and non-mated females were alike except that spermatozoa were usually found in smears from mated females on the first or second day after copulation. After oestrus, ovulation and corpus luteum formation occurred alike in mated and non-mated females. There were no differences between corpora lutea of pregnant and non-pregnant females. After parturition oestrus was inhibited by the onset of lactation except in one female which produced two successive young separated in age by approximately the length of one oestrous cycle. Females came into oestrus an average of 8\m=.\02\m=+-\0\m=.\18 days after removal of suckling young from the pouch.In pregnant females the gravid uterus was much larger than the non\x=req-\ gravid uterus from 12 days after oestrus until after parturition. The sub\x=req-\ epithelial capillary layer was better developed in the gravid than in the non-gravid uterus during the closing stages of pregnancy. The uterine luteal phase was present 7-8 days after oestrus and began to disappear at about 15 days after oestrus in both pregnant and non-pregnant females. There was no evidence that the luteal phase was longer in pregnant than in non-pregnant females and the occurrence of pregnancy did not extend the normal interval between successive oestrous periods if the young were removed at birth.

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Newborn young of the red kangaroo weighed about 750 mg. They had well‐developed nostrils and a large tongue and the forelimbs and digits of the inanus were well developed but otherwise the external features were embryonic. Sexes of the young were recognized when they were 14 to 20 days old. The young were firmly attached to the teat during the early part of pouch life, but one young removed from the teat at 43 days was able to re‐attach and another was found free when 70 days old. Observations relating to the appearance of body pigment, vibrissae and hair were made. Young about 150 days old were observed protruding their heads from the mother's pouch; they emerged temporarily at about 200 days and permanently at about 240 days. Young out of the pouch continued to suckle from the elongated teat they had used while in the pouch. Growth curves for the developing pouch young are given. In a non‐lactating female the interval between one oostrus, as diagnosed from the vaginal smear, and the next oestrus, at which mating occurred, was 37 days. The intervals between mating with the occurrence of fertilization, and post‐partum mating were 33 to 35 days. The gestation period was between 32 and 34 days. Fertilization occurred at post‐partum oestrus but the resulting offspring was not born while the earlier young occupied the pouch. If the pouch young was prematurely removed birth of a further young, resulting from post‐partum fertilization, occurred between 31 days 2 hours and 31 days 14 hours after removal. If the young was reared until it left the pouch birth occurred 230 to 252 days after post‐partum mating and in the absence of intervening mating. Parturition was observed five times in three females. During the hours before birth occurred pregnant females repeatedly cleaned the pouch by licking inside it. They also licked around the urogenital opening and one female licked the ventral surface between urogenital opening and pouch. Females sat on the base of the tail with the tail passed forwards between the hind‐legs, the legs extended forwards and the back supported by the enclosure fence while giving birth. Newborn young took about three minutes to reach the pouch after birth and there was no evidence that they were actively assisted by the mothers.

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