The age-related changes of the ciliary muscle of human eyes (33-87 years) were studied on histological meridional sections. Eighty-five melanoma eyes and 10 eyes of normal donors were investigated. The total area and the length of the muscle, the area of the three main portions and the distance of the inner apex of the muscle to the scleral spur were determined and correlated with age. Total area and length of the muscle show a continuous and significant decrease with age. The area of the longitudinal and reticular portion continuously decreases, whereas the area of the circular portion significantly increases with age. The decrease in area is more pronounced in the longitudinal portion than in the reticular portion of the muscle, which shows an age-related increase in connective tissue. In addition, the distance of the inner apex of the muscle to the scleral spur shortens continuously. Thus, with increasing age the ciliary muscle adopts an anterior-inward position. A similar form is seen in young eyes after ciliary muscle contraction only. There might be a functional relationship between the observed age-changes in the ciliary muscle system and the phenomenon of the so-called 'lens paradox' (steepening of the anterior and posterior curvatures of the disaccommodated lens with age).