The current study was conducted to determine the origin of stem cells during treatment of necrotic immature permanent teeth using blood clot regenerative endodontic procedure, and whether apical radiolucency has any negative influence on the treatment outcome both clinically and radiographically.Thirty teeth of twenty-four patients with necrotic immature permanent teeth were included in the current study which, were divided into two groups according to the presence or absence of periapical radiolucency. All patients were subjected to regenerative endodontic standardized protocol including minimal instrumentation, chemical disinfection using 1.5% NaOCl irrigant and Bimix intracanal medicament for 3 weeks.After subsidence of signs and symptoms, Bimix was removed by NaOCl irrigant followed by chelation using 17% EDTA for growth factors exposure and finally saline was dispensed inside root canals. Quantitative assessment of mesenchymal stem cells origin was conducted using molecular biology techniques, through investigating the gene expression of CD73 and CD105 using real-time RT- PCR. Saline samples were taken on sterile paper points just before bleeding induction and blood samples were taken immediately after irritation of periapical tissues using endodontic file to decide whether stem cells arise from disinfected pulp canal space or from periapical tissues delivered via bleeding induction.Comparison between the two groups showed the existence of both gene markers in both groups with and without radiolucencies as well as both saline and blood samples, however, with variable RQ values. Paired t-test was used for comparing the RQ values for both CD105 and CD73 in both saline and blood samples. In both