Biodegradable rods of polyglycolide or lactide-glycolide copolymer were used in the internal fixation of a variety of fractures and osteotomies in 516 patients. A clinically manifest foreign-body reaction occurred in 41 patients (7.9%), producing a fluctuant swelling at the implantation site after an average of 12 weeks. Spontaneous sinus formation or surgical drainage yielded a sterile exudate containing liquid remnants of the degrading implants. After prompt drainage this discharge subsided within three weeks. Histological examination showed a typical nonspecific foreign-body reaction with abundant giant cells both in patients with the reaction and in some patients with an uneventful clinical course. The factors determining the nature of the reaction were probably related to the local capacity of the tissues to clear the polymeric debris. The reactions did not influence the clinical or radiographic results, but recognition of the incidence and the features of the reaction is necessary in view of the increasing use of such implants.