The content and distribution of 1 alpha, 2 alpha, 3 alpha and M-collagens in human articular cartilage were studied. As controls, normal femoral heads and costal cartilage of autopsy material from newborn to 91-year-old persons were used. The osteoarthrotic cartilage was obtained from patients undergoing total hip replacement aged 45-80. The pepsin-digested cartilage collagen was fractionated by differential salt fractionation. The collagen content of the fractions was determined, and the fractions were separated by polyacrylamide slab gel electrophoresis. In the extracted collagen, the type II collagen varied from 82 to 97 per cent with increasing age. The 1 alpha, 2 alpha and 3 alpha chains decreased. M-collagen, especially of the high molecular weight components, disappeared with age. In osteoarthrosis three types of change - degeneration, new fibrocartilage formation on the surface of osteophyte and reparative cartilage - were separately studied. In all types of osteoarthrosis, an increase of minor collagens was found. In newly formed fibrocartilage, the reappearance of M-collagen was conspicuous. It is proposed that the three types of osteoarthrotic cartilage may be characterized on the basis of content and distribution of minor collagens.