Purpose: The primary objective of this pilot study was to evaluate the effectiveness of biphasic calcium phosphate (BCP) covered with a polyethylene glycol (PEG) membrane in the regeneration of 5-mm-diameter defects created in the calvaria of Wistar rats and compare this with the regeneration of defects covered only with the PEG membrane. Materials and Methods: Two 5-mm-diameter parietal defects were created in seven Wistar rats. The control defect in the left parietal bone was covered with an experimental PEG membrane (Straumann MembraGel); the test defect in the right parietal bone was filled with BCP (Straumann BoneCeramic) and covered with the same membrane. After a healing period of 2 months, the animals were sacrificed, and the samples were processed for histologic and histomorphometric analysis. Results: The test defects regenerated with BCP and covered with the PEG membrane had a percentage of new bone formation area of 61.7% ± 14.6%, and the control defects obtained mean new bone area of 57.3% ± 21.8%. The difference between groups was not statistically significant. The BCP did not reveal osteoconductive properties, and few particles were fully incorporated into the newly formed bone. The BCP maintained the space, and there was extremely low particle resorption during the healing period. The PEG membrane remained intact. Conclusion: There were no statistically significant differences between the test and control groups. BCP did not exhibit osteoconductive properties. Keywords: animal studies, biphasic calcium phosphate, guided bone regeneration, guided tissue regeneration, polyethylene glycol, Wistar rat