Objective: Clinicians have few quantitative studies that rank the in vivo pulp capping effects of commonly used restorative materials. These factors were investigated to provide guidance to clinicians. Method and materials: One hundred sixty-one standardized pulp-exposed cavities were prepared in nonhuman primate teeth. Exposed pulps were capped with calcium hydroxide, resin-modified glass-ionomer cements, and resin composites. Teeth were collected from 7 to 720 days to observe a full range of responses. Pulpal reactions were categorized according to the standards set by the International Standards Organization. Bacteria were detected with McKay's stain. Results: The incidence of bacterial microleakage was 19.7% with resin composite, 21.1% with resin-modified glass-ionomer cement, and 47.0% with calcium hydroxide. The severity of pulpal inflammation increased with the presence of bacteria or tunnel defects. The severity of pulpal inflammation prevented dentinal bridge formation at varying levels: slight for resin composite and resin-modified glass-ionomer cement, and severe with calcium hydroxide. The incidence of severe inflammation or pulpal necrosis was 7.9% with resin composite, 10.6% with calcium hydroxide, and 10.5% with resin-modified glass-ionomer cement. Other variables, such as pulpal exposure width and tertiary dentin formation, were not highly correlated to pulpal inflammation. Conclusion: Pulp capping with resin composite provided the lowest incidence of bacterial microleakage, the lowest levels of pulpal inflammation, and the lowest incidence of necrosis.