The wall thickness of the atherosclerotic common carotid artery may be quantitatively assessed by measuring of the intima-media thickness with high resolution B-mode ultrasonography. The reliability and reproducibility of a simple non-invasive planimetric method has been assessed. The interobserver, intraobserver, interreading and cardiac cycle dependent variabilities of intima-media thickness measurements in 150 randomly selected patients were evaluated. The mean absolute differences were 0.078 +/- 0.097 mm (interobserver), 0.064 +/- 0.052 and 0.048 +/- 0.05 mm (intraobserver), 0.016 +/- 0.037 and 0.018 +/- 0.038 (interreading), 0.072 +/- 0.076 and 0.054 +/- 0.061 (cardiac cycle dependent, pre-T and R-triggered). The results were satisfactory with coefficients of variation 13.1% (interobserver), 5.7-6% (intraobserver), 4-4.9% (interreading) and 7-8.5% (cardiac cycle dependent). This simple ultrasonic technique yielded highly reproducible measures of common carotid artery average intimal-medial thickness on the far wall and it appeared to be a reliable method for clinical investigations.