We have studied a series of natterjack populations with varying densities of adults on the three main habitat types (lowland heaths, coastal dunes and coastal marshes) occupied by this species in Britain. Animals were aged by skeletochronology, condition was assessed by measuring weight length ratios in autumn and home ranges were determined by individual-marking and by radiotelemetry. Female longevity was inversely correlated with population density, but no similar effect was observed for males. Uniformity of growth rates, absolute growth rates and mean condition for both sexes were also inversely related to population density, whereas mean home range showed a positive correlation. Taken together the data indicated that in high-density populations natterjack toads grew more slowly and erratically, were in poorer condition and foraged much more widely than their counterparts in low-density populations.