Abstract We have studied the effects of β-aminopropionitrile (BAPN) administration on the formation of spontaneous arterial lesions, characterized principally by a rupture in the internal elastic lamina (IEL) in the caudal and renal arteries of the Wistar rat. Treatment with BAPN (an inhibitor of lysyl oxidase) increased the formation of these lesions in rats up to 12 weeks of age but had differential effects on the caudal and renal artery in older rats. Administration of the nitrile to weanling rats led to the premature formation of lesions in caudal arteries of both male and female rats which morphologically resemble lesions which form spontaneously later in life. Dietary supplements of copper or pyridoxine were without effect on the formation of spontaneous caudal artery lesions when given from 5 wks of age but a copper supplement from midgestation slightly inhibited lesion formation only in male rats. This suggests that if copper deficiency is involved in spontaneous lesion formation, it is only a contributory factor. Quantification of either caudal or renal artery lesions within different litters of Wistar rats showed that there exists a familial aggregation in the frequency of spontaneous lesion formation, certain litters showing significantly higher levels of lesions than others. Adult Sprague-Dawley rats also appear to be more susceptible to the development of renal artery IEL defects than Wistar rats. The possibility of a hereditary disorder leading to a minor defect in elastic fibre structure which could be responsible for the spontaneous lesions is discussed.