A study of cartilage removed from the knees of twenty patients with rheumatoid arthiritis was presented. Specimens from ten normal patients were obtained as controls. In all of the rheumatoid joints no pannus was observed grossly. Under the microscope, however, pannus cells resembling those of rheumatoid synovium were found growing across the articular surface and penetrating the superficial layers in six of the rheumatoid patients. Cartilage cells in the deeper layers showed a variety of changes. Some were surrounded by large moats containing fibrillar material, others accumulated fat in their cytoplasm, while others showed a remarkable elongation of their cell processes. In all cases cell degeneration and death were prominent features. A discussion of the possible significance of these findings was presented.