PIP: Some of the characteristics of the process of mortality decline in Latin America were studied for the 1955-73 period. General characteristics of mortality decline were examined and total and cause specific standardized death rates were examined in an effort to uncover the contribution of changes in the incidence of some diseases to the rate of decline in the initial stages of the process. The relationship between socioeconomic factors and total and cause-specific levels of mortality were also examined. Data on deaths by age groups and causes on various Latin American countries were collected from regular publications of the World Health Organization (WHO). Only those countries for which information was available at least at 1 point during the 1950s and at least once during the 1960s were included. Adult deaths (above age 5) were adjusted for completeness using techniques by Brass (1975) and Preston (1979). Causes of deaths were grouped into categories that allowed the comparability of the 6th, 7th, and 8th revisions of the International Classification of Diseases. Death rates specific for 5-year age groups were computed. The analysis supports the idea that the major contributors to the rapid process of mortality decline were, in this order: infectious diseases, influenza-pneumonia-bronchitis, and diarrhea. Respiratory tuberculosis and other diseases of early infancy were responsible for about 12% of the total decline. Of late there has been an apparent increase in deaths due to cardiovascular diseases and neoplasms, but cardiovascular diseases (probably of infectious origin) may have contributed positively to mortality decline, perhaps as much as 28% of the total decline (net of the effects of changes in the category of "ill defined" deaths). The association between the decline in malaria and the concomitant decline in other infectious diseases points to a confirmation of the hypothesis which attributed substantial weight to medical innovations because of the synergism among the diseases themselves. The source of the changes in mortality were found to correspond in almost equal measure to rising standards of living and to the contribution of exogenous factors: about 45% of the changes between 1955-73 were due to rising standards of living. Exogenous factors seemed to have left a more decisive imprint among countries in which malaria was endemic and within categories of such diseases (such as infections) which were most likely to be controlled without imposing the necessity of substantial transformations in standards of living.