Although low levels of social support have been related to mortality from coronary heart disease, little is known about the role of social support among Mexican Americans. The authors therefore examined the relationship between social support and long-term survival in the Corpus Christi Heart Project. They developed a social support scale that used data collected during in-hospital interviews of 292 Mexican Americans and 304 non-Hispanic Whites who survived a myocardial infarction for more than 28 days. The scale incorporated three measures: marital status; if not married, whether living alone; and whether advised to seek help. During an average follow-up period of 43 months, 115 participants died. Survival following myocardial infarction was greater for those with high or medium social support than for those with low social support. With age, gender, ethnicity, education, employment, smoking, diabetes, hypertension, and hypercholesterolemia included in a proportional hazards regression model, the relative risk of mortality was 1.89 (95% CI, 1.20-2.97) for those with low social support. But when the two ethnic groups were analyzed separately, low social support was no longer a significant predictor of mortality for non-Hispanic Whites, whereas for Mexican Americans, the relative risk of mortality was 3.38 (95% CI, 1.73-6.62) for those with low social support.