Osteolysis is a radiographic term used to describe bone resorption adjacent to prosthetic implants. This process involves a spectrum of radiographic presentations, from small generalized linear patterns (linear osteolysis) to larger erosive patterns (aggressive osteolysis). The tissue from aggressive osteolytic lesions from five patients were compared with a series of linear osteolytic lesions from five additional patients. Total ribonucleic acid was extracted from these tissue samples, followed by reverse transcription and amplification by the polymerase chain reaction using a series of primers intended to amplify all ribonucleic acid species. The polymerase chain reaction products were separated by gel electrophoresis and compared by side by side analysis (differential display techniques). Transcription initiation factor IIB and cytokine receptor CRFB4 messenger ribonucleic acid were expressed in four of five patients with aggressive osteolytic lesions, as compared with none of five patients with linear osteolytic lesions. Conversely, nonmuscle myosin heavy chain messenger ribonucleic acid was expressed in five of five patients with linear osteolysis, and in none of the five patients with aggressive osteolysis. Thus, there is a difference in cell behavior between linear and aggressive osteolytic lesions that likely accounts for differences in radiographic appearance. This disparity is likely attributable to differences in local conditions (greater amounts of debris, increasing instability of the implant, or increased fluid pressures within the osteolytic lesions), and differences in host response.