Capture-mark-recapture and removal-trapping methods were used to monitor population parameters of Rattus fuscipes in cool temperate rainforest and dry sclerophyll forest. Population sizes, breeding, sex ratios, age structure, turnover, growth and condition were compared. Although significantly more rats were captured in the beech than in the sclerophyll forests, other demographic parameters were similar between the different populations. Numbers were highest in late summer and autumn, declined over winter and increased during spring and summer. Superimposed on this cycle, numbers differed between years; far fewer rats were present in the autumn of 1979 than in those of 1978 or 1980. The breeding season lasted from late spring to mid-autumn, and there were no apparent differences between the two habitats in breeding success, growth rates or condition, or in changes in the age-structure of populations with time. The young entered the population in summer and autumn and grew to adults through the winter and spring; the number of adults from the previous breeding season fell during the winter, and few survived to a second breeding season.