The level of blood lipids and apolipoproteins in subjects being screened for abdominal aortic aneurysms have been investigated. As part of an ultrasound screening programme in a population of 65- to 75-year-olds, blood samples were collected from 1460 of 1504 subjects with a normal aorta (97.1%) and 69 of 70 patients with an abdominal aortic aneurysm > 29 mm (99%). Samples were also taken from 22 of 27 patients (81%) with an ectatic aorta (26-29 mm). Total cholesterol, HDL-cholesterol, LDL-cholesterol, Apo-AI and Apo-B levels were significantly higher in women than in men (P < 0.01). Levels of HDL-cholesterol and Apo-AI were significantly lower in patients with an abdominal aortic aneurysm than in normal subjects (P < 0.001). The mean(s.d.) body mass index was 25.1(3.9) in women and 25.5(3.2) in men with aneurysms and not significantly greater than that of normal subjects (25.2(3.61) and 25.2(3.38) respectively).