Context:Vital pulp therapy has been known as one of the treatment options to preserve pulp after being exposed by trauma or caries.Aim:To investigate human pulpal response to white and grey mineral trioxide aggregate (WMTA, GMTA) and Dycal (MTA) as pulp capping agents.Setting and Design:Human volunteers were participated in this randomized clinical trial.Materials and Methods:This study was conducted on 90 intact first and second premolars of human maxillary and mandibular teeth. The teeth were randomly assigned into three groups of 30 each. Under local anesthesia, teeth were exposed and capped either with GMTA, WMTA, or Dycal. After 30, 60, and 90 days 10 teeth of each group were extracted and prepared for histologic observation.Statistical Analysis:Histopathologic data were analyzed by χ2, Kruskal Wallis and Mann Whitney tests.Results:the calcified bridge in teeth that were capped with GMTA was significantly thicker than Dycal at 30 and 60 days (P= 0.015 and P=0.002, respectively); whereas WMTA showed significantly thicker calcified bridge than Dycal at 90 days (P=0.02). In addition, GMTA specimens showed significantly less inflammation compared to Dycal samples at 90 days interval (P=0.019). No significant difference was found between GMTA and WMTA in terms of calcified bridge thickness and pulp inflammatory response to the capping materials (P>0.05).Conclusions:Based on the result of this study, both types of MTA can be suggested as the materials of choice for direct pulp capping procedure instead of Dycal as hard setting calcium hydroxide cement.