The percentage and numbers of CD8+ T cells are markedly decreased in peripheral blood from patients with arteritis temporalis. Transient cerebral ischaemic attacks (TIA) or brain infarctions have been frequently reported as the first and only clinical manifestation, and signs of carotid artery stenosis have been reported in 15-20% of patients with arteritis temporalis. We used a determination of the CD8+ T-cell subset to evaluate patients with TIA. Concentrations of CD8+ T cells were measured in the peripheral blood of 24 patients with TIA. The cohort investigated was consecutive, but adjusted to have a 50% a priori probability of carotid artery stenosis. An ultrasound Doppler investigation of the carotid arteries was performed in all patients. Controls were 24 healthy subjects of comparable age and sex. Median percentage and concentrations of CD8+ T cells were significantly lower in patients with TIA and carotid artery stenosis compared with (1) patients with TIA and no carotid stenosis (CD8+ %: 13.5 vs 26; CD8+ x 10(9)/1: 0.24 vs 0.44, P < 0.001) and (2) healthy controls (CD8+ %: 13.5 vs 22.5; CD8+ x 10(9)/1: 0.24 vs 0.52, P < 0.001). The prevalence of a carotid artery stenosis in the combined first and second quartile of CD8+ % (CD8+ % <or= 15) was 80% (95% CI: 44-97%) and in the combined third and fourth quartile 28.5% (95% CI: 8-58%) (P = 0.03). The positive predictive value for carotid artery stenosis was 80%, an incremental ruling in gain of 60%. The negative predictive value was 71%. In patients with TIA and carotid artery stenosis, a reduced percentage and numbers of the CD8+ T-cell subset were significantly more frequent than in patients with no stenosis. No other signs of arteritis temporalis were found.