Two studies showing an influence of workload on myocardial infarction (MI) incidence in workers were conducted. In an attempt to determine the predictive power of a combination of subjective and objective risk variables, a prospective study of 41 to 61 year old construction workers was conducted. All of those surveyed had had no work absenteeism greater than 30 consecutive days. Responses were subjected to a factor analysis. Persons responding positively to questions regarding extra work, responsibility, problems, conflicts in the job, or threat of unemployment during the preceding 12 months were considered to be at greater risk of MI. A 2 year follow-up was performed. Of the MI group, 37% reported a work problem the preceding year. On the other hand, 48% of those stating they had no work problems the preceding year suffered MI. In another study, male monozygotic (18 pairs) and dizygotic (13 pairs) aged 52 to 74 years (mean 63), often discordant with regard to ischemic heart disease manifestations (monozygotic not significantly less discordant than dizygotic), were subjected to a long resting period and then to a psychiatric interview, during which the majority of subjects revealed conflicts regarding childhood, work or present family situation. Intrapair variance of circulatory measures during rest and during psychiatric interview among dizygotic pairs divided by the same monozygotic intrapair variance is shown. The dizygotic pair members are more dissimilar than the monozygotic pair members for diastolic and systolic blood pressure and peripheral pulse volume (vasodilation and vasoconstriction) during interview but not during rest. This indicates that heredity may be more important for blood-pressure level during psychological strain than during rest. To judge from this, heart-rate is determined to a great extent both at rest and during interview by heredity, whereas the blood pressures have insignificant correlations at rest but around 0.65 during interview, accounting for about 40% of the total variance.