Fourteen patients (six males, eight females; mean age, 20 years) with homocystinuria due to homozygous cystathionine-beta-synthase (CBS) deficiency, underwent a vascular examination. Fourteen heterozygotes (seven males, seven females; mean age, 46 years), including 12 parents and one daughter of homozygotes (obligate heterozygotes), and one sister of a homozygote (with low enzyme activity as evaluated in vitro), were also examined. Homozygotes and heterozygotes were compared with two separate control groups of different age (mean age, 20 and 43 years, respectively). Ankle/arm systolic pressure index (by continuous-wave Doppler) was, on average, lower in homozygotes (P less than .01) and heterozygotes (P less than .05) as compared with the controls. An ankle/arm index less than 0.97 and suggesting flow-reducing arterial lesions was found in six (21%) lower limbs of homozygotes versus zero in controls (P less than .05). Echo Doppler (Duplex Scanner) abnormalities, indicating early, non-flow-reducing lesions of iliac arteries were more frequent in homozygotes (seven wall abnormalities or stenoses less than 15%) than in young controls (P less than .05). The corresponding figures for heterozygotes were seven wall abnormalities or stenoses (1% to 15% and one stenosis 16% to 50%) (P less than .01 v middle-aged controls). Early lesions (three wall abnormalities or stenoses less than 15%, three stenoses 16% to 50%) were detected in six (23%) internal carotids of heterozygotes versus three (3%) of corresponding controls (P less than .05). Technical limitations precluded the accurate detection of early lesions in the internal carotid arteries of young homozygotes and controls.(ABSTRACT TRUNCATED AT 250 WORDS)