A higher than expected number of violent deaths and suicides in coronary prevention trials has provoked interest in the possibility that low serum cholesterol concentrations are associated in the general population with personality characteristics predisposing to aggressive and suicidal behaviour. We have investigated this possibility in the Edinburgh Artery Study. We measured serum lipid concentrations in blood samples taken from fasting subjects and assessed personality characteristics on the Bedford Foulds Personality Deviance Scales in a random sample of 1592 men and women aged 55-74 years, selected from age-sex registers of ten general practices in Edinburgh. Serum cholesterol concentration was not significantly associated with aggression in men, but it was associated in multivariate analysis (though not univariate analysis) with denigratory attitudes towards others among women. However, serum triglyceride concentration was related, especially in men, to hostile acts (r=0·13, p<0·001) and domineering attitude (r=0·12, p<0·001) independently of age, total and HDL cholesterol, cigarette smoking, and alcohol consumption. Subjects taking part in prevention trials have higher triglyceride concentrations than the general population and the relation between serum triglyceride concentration and aggression merits further investigation.