Although sentiments about the positive health benefits of regular exercise have been expressed for many centuries, it is only in the past three decades that epidemiologic evidence has provided scientific support for the health benefits of being physically active. The evidence for the protective effect of physical activity is particularly strong with reference to cardiovascular disease, with the relative risk of being "inactive" compared to 'active' estimated to typically lie between 1.5 and 2.0. Despite the popular view that exercise participation has increased in recent years, estimates of trends in physical activity in Australian (and other) populations have been difficult to interpret because of the different measurements and surveys used. We examined data from population surveys using well validated, standardised methods to assess exercise participation, through National surveys between 1984 and 1987 conducted by the Commonwealth Department of the Arts, Sport, the Environment, Tourism and Territories (DASETT). Over the period in which the surveys were conducted, there appears to have been a slight increase in the proportion of Australians who participated in regular physical activity. There was a significant decline in the proportion who reported being totally sedentary--from 32.9 per cent in 1984 to 25.4 per cent in 1987. The data from all of the surveys were then pooled to give an overall sample size of 17053, and socio-demographic variables were examined in relation to exercise participation. Women, older people, the less well educated, and those on lower incomes were less likely to perform regular physical activity. Inequalities in the social distribution of exercise participation parallel those found for other health risk factors.(ABSTRACT TRUNCATED AT 250 WORDS)