The effects of calxyl, ZOE, zinc oxide without eugenol, and zinc oxide with an antibacterial substance (glutaraldehyde) were tested on perforated molar pulps of rats. All of the substances tested were found to lead to the same initial reactions (acute inflammation and partial necrosis). Calxyl and ZOE yielded unfavorable results. There was a negligible tendency of the pulp toward hard tissue demarcation. Zinc oxide without eugenol improved the formation by the pulp of secondary tin. - The use of glutaraldehyde resulted in a less pronounced spread of inflammation as well as in the formation of new hard tissue in one half of the cases. Molars of rats are particularly suitable for biologically examining the local toxicity of pulpal protectives and the regeneration of the pulp. The results presented in this paper are discussed from the point of view of pulp-preserving therapy and of avoiding invasion by germs.