An attempt is made to explore and explain the impact of social changes on mortality decline. The work has been part of a 4 yr project in 9 villages of Karnataka, South India. Anthropological and survey approaches were used. Mortality continued to fall long after control of the major epidemic diseases had been achieved, although no addition had been made to the existing modern medical facilities. These facilities still attract only a fraction of the patients that might be expected from the experience of countries in which mortality is low and disproportionately few very young or old persons attend. Most treatment given followed neither the methods of modern nor those of ayurvedic medicine, the identification of the type of illness and subsequent treatment depended on the fundamental belief system of the villages. The change to modern medicine is one aspect of the secularization of society. Social, especially educational change, alters not only beliefs about treatment, but also the power structure involved in deciding the timing and type of treatment given. The type of treatment is also partly determined by its cost. Components of mortality decline, such as nutrition, which do not depend on the treatment of disease, were also explored. Social change has almost certainly played a major role in the reduction of mortality in many societies.