Hemolytic property is a specific feature of bacteria to obtain iron which is essential for its survival in host tissues. Therefore, it is thought to be one of several factors of virulence. The purpose of this study was to investigate the hemolytic properties of Prevotella nigrescens isolated from the teeth diagnosed as pulp necrosis and apical periodontitis under the presence of hemolysin inhibitors such as NaN₃ and dithiothreitol, heat, various pH and cultural conditions.

The results were as follows;

1. Clinically isolated P. nigrescens strains and standard P. nigrscens ATCC 33563 showed hemolytic activity.

2. P. nigrescens showed higher hemolytic activity against human erythrocytes than sheep or horse erythrocytes.

3. NaN₃ and dithiothreitol (DTT) reduced the hemolytic activity of P. nigrescens in a dose dependent manner (p < 0.05).

4. Optimal pH for the maximum hemolytic activity of P. nigrescens was 4.0 and the hemolysin was stable under the 50℃, but the hemolytic activity was significantly decreased at 95℃.

5. P. nigrescens cultured in 10% CO₂ condition showed higher hemolytic activity than the bacteria cultured in the anaerobic condition.