This in vitro study correlates morphologic and radioimmunoassay (RIA) findings on the effects of elastase on the elastic fibers that are found in the rabbit craniomandibular joint (CMJ) articular disk. Articular disks were removed from rabbit CMJs at necropsy, and cut sagittally into two pieces which were incubated in 0.3 ml of phosphate-buffered saline containing either 0, 12.5, 25 or 50 units of porcine pancreatic elastase for either 1, 3 or 24 h. The quantitative RIA findings correlated well with the qualitative light-microscopic observations in that both methods showed a reduction in the amounts of elastin in the CMJ disks following enzyme treatment. However, the morphologic appearance of most of the elastase-treated disks suggested that the destruction of the elastic fibers was more extensive than was suggested by the results of the RIA which indicated that some elastin remained in the tissues of the disks even when the highest enzyme level and longest incubation period were combined. The results of this study also support the interpretation that the resorcin-fuchsin-stained fibers in the rabbit CMJ disk are elastic fibers.