of formal rationality and idcas about lifestyles in general are applied to current trends in health lifestyles. The central contribution of Weber's thinking is recognition of thc dialcctical intcrplay bctwcen formal versus substantive rationality, consumption versus production, choice versus life chances, class similarities vcrsus distinctions, and self-control vcrsus conformity in shaping health lifestyles and the reality of their operationalization in the postmodern world. In a largely applied subdiscipline like medical sociology. Weber's work offers a theoretical background on which to enrich our understanding of health lifestyles and grapple with the initial theoretical challcngcs poscd by lifcstylc rcscarch.The usefulness of classic sociological theory in explaining social change in today's world has not always been apparent, despite the fact that, as Parsons (1981) observed, one can often learn something new by returning to the classics. The goal of this article is to apply Weber's theory of formal rationality--one of the major paradigms of sociological thought-and his general ideas about lifestyle to the concept of health lifestyles. This approach allows us to acquire new insights into an. important emerging feature of postmodernity, namely, the growing dominance of formal rationality in health matters.We argue that formal rationality (the purposeful calculation of the most efficient means to an end) is a more dominant aspect of health-lifestyle participation in postmodern society than substantive rationality (an orientation toward ideal values and ends). Whereas the rationality behind health lifestyles in the past tended to be more substantive (reflecting the value of health as an ideal state), it has become more formal (the most effective method for individuals to look better, enjoy increased vitality, and enhance life expectancy). What this trend signifies is that a distinctive aspect of postmodernity is greater personal control over one's health and-consistent with Ritzer and Walczak's (1988)