Radio-tracking and mark recapture methods were used to characterize the spatial organization and temporal activity patterns of free-ranging platypuses in southern Victoria. The study area supported an estimated 1.3-2.1 adult or subadult animals per kilometre of stream in the three summers sampled. The individual home ranges of 15 radio-tagged animals comprised 0.33-2.28 km of stream; animals foraging exclusively in the stream had significantly longer ranges (mean=1.40 km) than animals which also foraged in associated pond habitats (mean=0.64km). Home ranges of grown females overlapped with those of neighbouring grown females, subadult and adult males, and juveniles (<l y old) of both sexes. While the home ranges of a subadult and adult male, and subadult and juvenile male also overlapped substantially, only one sexually mature male was trapped at any given point in time, suggesting that adult males may occupy mutually exclusive home ranges in the study area. Most platypuses were observed to den at more than one location: burrow sharing was recorded in the case of a subadult and adult male, two grown females, a grown female and independent first-year female, and two independent first-year females. The mean length of time that nine individuals spent in dens per resting period varied from 11.6-16.7 h. In addition, two grown females remained inactive in dens for longer periods (3-6.5 days) in late May-June.