1.The ramification,distribution and collateral circulation of the intraorganic renal arteries have been studied in 130 kidneys from adults and children by means of dissection, injection of casting material or arteriography of fresh kidneys. 2.The intraorganic renal arteries were characterized by a segmented arrangement. The study of arterial casts and of individual segments injected with differently colored acetone-celluloid solution and of segmental arteriogram has shown that there is no col- lateral circulation between adjoining segments.According to the distribution of the ar- teries studied,the kidney is in most cases divisible into five segments—the apical,upper, middle,lower and posterior. 3.In 85.0?3.25% of cases the renal artery is single.Its primary divisions may be distinguished into certain types,among which the anterior-posterior(65.69?4.70%) and superior-inferior(23.53?4.20%)are of the most frequent occurrence.In the former, the anterior division usually gives rise to the apical,upper,middle and lower segmental arteries,while the posterior division continues as such into the posterior segment.In the latter,the superior division usually gives rise either to the apical,upper,middle and posterior or to the apical,upper and posterior,while the inferior division continues as the lower segmental artery or gives rise to middle and lower segmental arteries. Variations in the number,origin and distribution of the apical and lower segmental arteries have been described. 4.When two renal arteries are present instead of one,in 70.58?11.05% of cases, the accessory renal artery continues as the lower or apical segmental artery,while the main stem gives off the other segmental arteries. 5.The manner of branching of the primary division was classified into “main stem” and “dispersed”patterns.In the anterior half of kidney the “dispersed”pattern is most prevalent,whereas in the posterior half the “main stem”occurs more frequently.We have also found that the branching pattern is in close correlation with the external form of the kidney or the shape of the lips. 6.The sites at which the segmental arteries enter the renal parenchyma at the hilus are more or less regular.The location of the sites may be classified into three groups.