Numbers of deaths from coronary heart disease (CHD) and cerebrovascular disease (CVD) were available for five years (1980-84) in the North and South Islands of New Zealand; estimated death rates were determined, and age correction made. There was a major seasonal variation by month in coronary and cerebrovascular deaths in both sexes and both islands, with a zenith in June/July/August (winter) and a nadir in December/January/February (summer). There was a less obvious, and less complete, linear trend, with declining secular (annual) mortality over the five years. This was more obvious in North Island but not proven in South Island. After standardising for age, coronary mortality rates (but not cerebrovascular mortality rates), were significantly higher in South Island than in North Island. Mortality from both CHD and CVD was significantly higher in males than in females.