The relationship between smoking and vascular disease requires reliable information on the smoking status of patients suffering these disorders. As self-reported smoking status is unreliable and therefore misleading, biochemical markers (such as serum thiocyanate) provide a more accurate guide to smoking status. This study compared the self-reported and biochemical marker data (serum thiocyanate) for two different groups: 215 patients with peripheral vascular disease (PVD) and 124 with ischaemic heart disease (IHD). The object of the comparison was to assess if there was any difference between the two groups with regard to denial of smoking. The PVD group had more smokers by either criterion (verbal 34% in PVD, 15% in IHD, P < 0.001: thiocyanate level > 12.5 micrograms ml-1, 47% in PVD, 34% in IHD, P < 0.05). Of those verbally claiming and biochemically assessed as smokers, 55% of those with IHD and 28% of those with PVD denied using cigarettes. Our data point to differences in verbal reporting of smoking between patients with IHD and PVD. This probably reflects the patient's perception of the dangers of smoking and their diseases and may have clinical consequences for the collection of accurate data on the influence of this risk factor on atherosclerosis.