The depth of our current knowledge of the dose-response gradient for physical activity and health is highly variable across the different health parameters. To the extent that the existing literature allows conclusions, it appears that (a) most health parameters are related to the amount of habitual physical activity in a graded fashion; (b) intensity of physical activity may be independently related, in a graded fashion, to some health parameters but unrelated to others; and (c) for some variables, the dose-response relationship is linear but, in other cases, is curvilinear. At present, these conclusions must be considered tentative, and most experts agree that further elucidation of dose-response relationships should be a major thrust of future research on physical activity and health.