Peripheral arterial occlusive disease is occasionally observed in young adults. In these patients thromboembolic events are a menace and life expectancy is reduced. We studied two fibrinolytic factors, tissue plasminogen activator (t-PA) and plasminogen activator inhibitor (PAI-1), possibly risk factors for an early onset of the disease or for complications, in 75 patients seen at the out-patient clinic with symptoms of arterial occlusive disease manifest before the age of 45 years and we compared them with an age and sex matched control group of 29 ambulant patients with minor surgical problems. In both groups we looked for a correlation with plasma insulin, C-peptide, body mass index, von Willebrand factor, and triglyceride levels, parameters of the insulin resistance syndrome, and smoking. In the patients with occlusive arterial disease PAI activity and t-PA antigen were both significantly higher, and t-PA activity significantly lower than in the control group. An unfavourable effect on the disease is surmised. In a subgroup of heavy smokers, PAI activity, body mass index and triglycerides were significantly higher than in light smokers (less than 30 000 cigarettes in their life) or non-smokers. This suggests that the high PAI-1-levels are, at least in our patient population, associated with smoking. A warning against smoking is warranted in atherosclerosis prone subjects, especially in members of affected families. Plasma insulin and C-peptide levels were not statistically different in the two groups, but the positive correlation of PAI activity with insulin and C-peptide levels, and a positive correlation with triglycerides and body mass index, suggest a relationship of peripheral atherosclerosis with the insulin resistance syndrome, a hitherto unnoticed association.