In most industrialized countries, mortality in general, and cardiovascular disease mortality in particular, have shown decreasing trends since around 1970, following stagnation or increases observed during the 1950s and 1960s. In some countries, however (e.g. in Eastern Europe), male mortality from cardiovascular diseases increased during recent years. The levels and trends of mortality from cardiovascular diseases vary considerably among countries. Measured in terms of age-standardized rates, the ratio between the highest and the lowest rates around 1985 was about 2 for total mortality but about 4 for all cardiovascular diseases combined. With further breakdowns the ratio was even greater, i.e. 4-5 for heart diseases and 6-7 for cerebrovascular disease. For ischaemic heart disease alone, the ratio reached as high as 10, though part of this wide range should be attributed to artefacts due to the varying diagnostic practices followed in different countries. The speed of mortality changes also differed among countries, ranging from a rapid decrease to a rapid increase. In general, the trends were much more favourable in females than in males. Consequently, sex differentials have been widened. The male/female ratio in mortality for ischaemic heart disease has now exceeded 3 in a number of countries. The ratio for cerebrovascular diseases, which used to be close to 1 in many countries in the early 1950s, has also increased, often reaching the level of 1.5 or higher. Differentials were observed also among different age groups in some countries. There seems to be a tendency for mortality change, either an increase or a decrease, to be quicker in younger age groups than in older ones. These varying levels and trends in cardiovascular disease mortality have no doubt been caused by a multitude of risk factors operating in each country, affecting the incidence of cardiovascular diseases and their prognosis. Much is already known about these risk factors and about the measures to be taken by the health services as well as by individuals for prevention and effective therapy. The considerable variation in mortality levels and trends observed among different countries points to the possibility for action by countries heavily affected by cardiovascular diseases. Mortality surveillance in each country and at the international level thus reveals how each country's situation and trends compare with others and provides a basis for action and further research. Progress in WHO's MONICA (MONItoring of trends and determinants in CArdiovascular disease) project will clarify various aspects of the role played by risk factors in different communities.