The authors used 35S-sulfate and 3H-proline to trace labeled molecules in autoradiograms of aged monkey and human macular retina to detect the synthesis of extracellular matrix (ECM) components by retinal pigment epithelial (RPE) cells. Quantitative analysis of silver grains 6 hr and 3 d after intravitreal injection of 35S-sulfate in the monkey showed that secretion from the basal pole of the RPE occurs at a slower rate than from the apical pole. In vitro incubation of human maculas produced poor autoradiographs with 35S-sulfate. Good autoradiographs were obtained using 3H-proline. Human macular RPE showed uneven labeling, but densely labeled cells did not correlate with sites of basal linear deposits, ECM though to be basement membrane material, and a hallmark of age-related maculopathy. The time course of labeling in adult primate tissue showed a fairly high turnover rate for these molecules. Scant labeling of ECM at drusen sites and no labeling in basal linear deposits suggested that either (1) these structures have a slow turnover or (2) their components contain scant sulfate and proline. Alternatively, faulty degradative processes rather than enhanced synthesis may account for the accumulation of abnormal ECM at the RPE-Bruch's membrane interface in aged maculas.