Drusen are yellowish deposits at the level of the retinal pigment epithelium and are frequently associated with age-related maculopathy (ARM). Drusen often change in size and number over time and may be followed by atrophic or exudative macular degeneration. A quantitative method to measure the development of drusen is needed for controlled studies of the natural history, prognosis, and treatment of ARM. An objective method is described using computer image analysis of fundus photographs for the detection and measurement of drusen. This technique enables us to measure both the area of drusen in the macula and the changes in the drusen pattern over time. Evaluation of repeated photographs showed reproducibility of 6.1%, whereas the reproducibility of processing photographic duplicates was 2.3%. Digitization with a high-quality linear array solid state camera did not change reproducibility significantly.