In this study, the changes of canine pulpal vascular architecture, at various stage of growth when subjected so acute and chronic inflammation were examined through a scanning electron microscope using vascular corrosive resin casts. The following results were obtained. 1. The sites of leakage of MMA resin out of the blood vessels coincided with the site where microleakage occurred, thus suggesting that resin cast method is a useful technique to study the area where vascular permeability was increased. 2. In an acute inflammation, leakage of resin out of blood vessels was mainly observed at the sites of venular network (VN) and venous capillaries, and these could be discriminated by use of the casts method. This is in accordance with the result by Tsuchiya, Magino and Palade, where they showed that vascular permeability was preferentially observed in venule and venous capillaries. 3. In pulp with a lesser number of venules during the stage of late maturation, leakage of resin was observed from those surviving venules to the bundle of main blood vessels. 4. Leakage of resin was not observed in the terminal capillary network (TCN), but in the capillary network (CN) and VN, especially just beneath the dentin, where cavity preparation with a water spray was performed. Accordingly, the generation of heat during cavity preparation was thought to be the main reason for disturbance of the pulp. 5. Severe case of suppurative and chronic ulcerative pulpitis were generated within one week after cavity preparation. The vascular architecture was characterized by a dense granular capillary network facing the ulcerative surface. 6. One week after pulpal exposure, at the stage of early maturation of pulp, the granulated blood vessels located within the exposed pulp had a tendency to shift to a pulp polyp. And the granulated blood vessels after two months showed a pulp polyp. 7. At the late maturation stage of pulp, development the pulp chamber and dentin tubules were saturated by resin cast method, suggesting the possibility of leakage out of blood vessels and the death of some odontoblasts. The pulp at this stage shifted to a gangrous pulp. 8. In conclusion, the pulpal vascularity constantly undergoes morphologic changes incidential to various condition such as growth, maturation and inflammation. Basically, vascularity of dental pulp consists of three major layers, that is TCN, CN and VN. When it comes to the maturation stage, owing to the apposition of secondary dentin, the pulp cavity will become narrow and the vasculation within it will undergo a histologic change. As a result, most of the VN disappears.(ABSTRACT TRUNCATED AT 400 WORDS)