Changes in summer (July-September) and winter (January-March) mortalities of people aged 70-74 in England and Wales from 1964 to 1984 were compared with possible causal factors. Summer mortalities were little affected by annual temperature or influenza epidemics and fell from 1972-1975 for all causes, coronary and respiratory causes, while cerebrovascular mortality fell more rapidly from that time. Cigarette consumption also fell from 1972-1975; falling consumptions of total fat from 1970 and saturated fat from 1972-1975 probably also contributed to the fall in arterial deaths, and likewise falls in prescription rates for tranquillisers and sedatives from 1976-1978 to the fall in respiratory deaths. From 1964 to 1984 use of central heating increased from 13% to 69% of households, domestic fuel consumption increased, and excess mortality in winter from respiratory disease declined by 69%, even relative to summer mortality and when adjusted for varying coldness of winters. The improvement was partly explained by a decline in influenza epidemics. By contrast, excess mortalities in winter from coronary and cerebrovascular disease, although rising in some early influenza epidemics, did not fall significantly as home heating improved. These thrombotic deaths together accounted for 56% of the total excess winter mortality by 1984. The findings support other indications that most of the excess mortality from arterial thrombosis in winter in England and Wales is due to brief excursions outdoors rather than to low indoor temperatures.