The pulps of 40 permanent teeth of two monkeys were mechanically exposed and contaminated with adjacent saliva or plaque for 3 to 5 1/2 hours. The pulps were then capped with either Keflin (an antibiotic), Durelon (a polycarboxylate cement), or Dycal (a calcium hydroxide compound). Varnish and then amalgam were inserted. Each monkey received at least one dose of Procion red H-8BS vital dye. The teeth were extracted from one monkey 23 months after capping and from the other monkey 29 months after capping. Serial, decalcified, 7 mum-thick paraffin sections were prepared. Alternate slides were stained with hematoxylin ane eosin. Unstained sections were examined for Procion labeling, and selected slides were stained by the Brown-Brenn method for bacteria. Of 13 teeth capped with Keflin, only 4 responded satisfactorily. All of the Dycal and Durelon-capped pulps were successful at both time intervals. All of the Dycal-capped pulps showed complete bridging and no inflammation or pulp obliteration. Bridging was complete in only three of the Durelon-capped pulps. The findings of this study support the findings in our previous study3 and further substantiate the effectiveness of Dycal as a pulp-capping agent. The often-repeated claim that calcium hydroxide compounds exert a persistent stimulating effect on the pulp resulting in its eventual obliteration was not supported. Durelon is not recommended for pulp capping since the material apparently lacks an antibacterial effect and does not stimulate reparative dentinogenesis at the exposure site. The low rate of satisfactory responses of pulps capped with Keflin, as used, precludes its use of pulp capping.