Nonspecific myocardial changes were studied in 1357 aboriginal males, aged 20 to 59 years and living in 4 different climatic and geographic regions of Mongolia. ECG analysis and interpretation was based on the Minnesota code (3-2, 5-1, 5-2, 5-3). Nonspecific changes in the T wave, STj and ST segment were particularly frequent in records from leads V1-4, and minimal in records from the left chest leads (V5-6). These features were detected in 21.9 +/- 2.7% (p less than 0.01) of the Khangai population, 14.6 +/- 2.2% (p less than 0.01) of the Gobi-Altaic population, 6.0 +/- 2.8% in mid-altitude people, and 4.0 +/- 1.2% in low altitude ones. A comparison of the two former, high-altitude, populations showed the changes to occur more frequently (by 7.3%) in Khangai population, as compared to Gobi-Altaic residents (p less than 0.05), suggesting that the development of nonspecific myocardial changes is influenced by other, more forceful, factors, such as cold, as well as the altitude factor. The incidence of nonspecific myocardial changes increases with age. Differential diagnosis of coronary heart disease should use exercise testing in addition to the Minnesota code criteria.