Stereological analyses of the distribution of capillaries in skeletal muscles of congenitally dystrophic mice are described and reported. Two methods are used, each based on a different mathematical model of the 3-dimensional distribution of lines in space. For these analyses specimens of extensor digitorum longus muscle from clinically affected C57BL/6Jdy2J/dy2J dystrophic mice, and from non-littermate controls, were used. The analyses were carried out on transverse and longitudinally orientated semithin sections of these muscles. Although the two methods employed are based on different mathematical models and yield results relevant to each particular model, it is clear that there is a more extensive capillary network present per unit volume of the dystrophic muscle than in control muscles. These findings are relevant to the theories which involve a vascular aetiology for muscular dystrophy. It is apparent that, in order to explore the structure of the capillary network more fully, there is a need for the development of more sophisticated stereological techniques for analysis of capillaries in skeletal muscle.