There has been clinical concern about the gray discoloration in synovial tissue adjacent to carbon-reinforced polyethylene total joint implants. To evaluate the pathologic response of the synovium to this material, synovial specimens from 11 total ankle cases with carbon-reinforced tibial components and two synovial specimens from cases with standard polyethylene tibial components were studied by gross and histologic techniques. Polyethylene debris was found to produce a significant synovial reaction with histiocytes and foreign body giant cells. This was found in both the carbon-reinforced cases and in those cases without carbon-reinforced components. This reaction is also seen in revisions of total hips and total knees in which standard polyethylene components have been implanted. In contrast with this, carbon particles produced only a minimal reaction in the synovial tissue. Carbon appears to be an extremely benign implant material, and synovial discoloration from shed carbon fibrils does not appear to present a significant clinical problem.