We calculated acute myocardial infarction and chronic coronary heart disease mortality rates for Mexican Americans and non-Hispanic whites in Texas for the 10-year period from 1980 through 1989 in an examination of ethnicity-related differences in death rates and trends according to vital statistics for the state of Texas. During the study period, acute myocardial infarction mortality decreased significantly in all four sex-ethnic groups, between 5.1% and 7.4% per year. Chronic coronary heart disease mortality rates decreased less, but significantly, for women in both ethnic groups, decreasing 3.4% and 1.8% per year for Mexican-American and non-Hispanic white women, respectively. We found no significant trend of changes in chronic coronary heart disease mortality rate among men in either ethnic group. For both acute myocardial infarction and chronic coronary heart disease mortality, rates were significantly lower among Mexican-American men than among non-Hispanic white men. Age-adjusted rate ratios for Mexican-American men in relation to non-Hispanic white men were 0.78 (95% CI: 0.65-0.93) and 0.75 (0.65-0.86) for acute myocardial infarction and chronic coronary heart disease mortality, respectively. No significant ethnicity-related mortality difference was seen among women. This previously observed interaction of ethnicity and sex in relation to coronary heart disease mortality remains unexplained. Despite apparently adverse cardiovascular risk factor profiles, Mexican Americans have acute myocardial infarction and chronic coronary heart disease mortality rates equal to or lower than their non-Hispanic white counterparts on the basis of death certificate data. This paradox deserves further attention.