The effect of current shift and recent shift change, on risk of contracting ischemic heart disease, was studied among workers at heavy equipment factories. A nested case/control study was conducted in a cohort of 21,000 men at four heavy equipment factories. The study compared 163 men who died of ischemic heart disease at work or within a week of having worked to control workers. The cases had no prior history of heart disease. Each case was matched with five controls, based on age, factory and race. Shifts worked by cases and controls were determined from personnel records. Data were analyzed by conditional logistic regression with retained matching. Mean time worked on the current shift, at the time of case death, was 9 years, with 72% of study subjects working on the first shift, 22% on second shift and 6% on third shift. Differences in heart disease associated with current shifts were not detected. Recent change from second or third, to first shift lowered the risk of heart disease initially, but the effect decreased with time. There was no corresponding negative effect associated with changing from first to second or third shifts. The authors conclude that there was little evidence for effects on risk of death from heart disease, due to current shift. Their data suggest a temporary lowering of risk after change from second or third to first shift.