The tammar wallaby, Macropus eugenii, has a seasonal breeding cycle which is dependent upon the light regime. Females normally produce one pouch young a year, while carrying a diapausing blastocyst in the uterus. Before the winter solstice, the sucking stimulus of lactation is responsible for inhibition of blastocyst development (lactational quiescence); after this time, inhibition is caused by increasing day length (seasonal quiescence). Lactational quiescence can be broken by removal of the developing young in the pouch, and seasonal quiescence by artificial light regimes, or melatonin treatment; administration of the drug bromocriptine breaks diapause between April and September. Gestation is approximately 28 days and birth is followed by postpartum mating. Hence in theory these interventions can be used to produce up to 12 young per female per year, raising the possibility that the species can be used for genetics. It has a 2n=16 karyotype. In common with other marsupial species, the tammar possesses low allozymic and serum protein variability within the Kangaroo Island population (4/41 loci polymorphic, average heterozygosity of 0.012). However, there are 5/32 fixed differences between the Kangaroo I. and Garden I. tammar populations. Individuals from these two populations will hybridise, although the fertility of the hybrids has yet to be examined. A highly polymorphic major histocompatibility locus exists. A total of 14 loci is probably involved for both intrapopulation and interpopulation markers. We propose to use the species for comparative gene mapping and to see whether sex differences in recombination exist.