Risk factors for intermittent claudication (IC) were studied in 54 patients--that is, all patients with IC on the lists of two general practices--and 108 controls. Smoking was the factor most strongly associated with the development of IC, but systolic and diastolic blood pressures and concentrations of triglyceride, urate, and fibrinogen were all significantly higher among the patients with IC than the controls. The presence of more than one factor appeared to be associated with a multiplicative increase in risk. Cholesterol, an important risk factor for ischaemic heart disease, was not associated with an increased risk of IC. IC was present in about 2% of the men and 1% of the women, who were aged 45-69 years. These findings suggest that IC, a common and disabling manifestation of atheroslcerosis, may be largely preventable.