Lysis of erythrocytes isolated from human, rabbit, and mouse blood samples was investigated with the culture supernatant of Xenorhabdus nematophilus in a primary form. Prior to use, the culture supernatant of the bacteria was concentrated and the concentrate was dialyzed against Tris-HCl buffer (10 mM, pH 8.1) by ultrafiltration using PM-5 membrane with a molecular weight cut-off of 5,000. At $30^{circ}C$, the supernatant exhibited no lytic activity towards three types of erythrocytes. However, at $4^{circ}C$, the supernatant showed selective lytic activity towards rabbit erythrocytes within 90 min. yet did not lyze human or mouse erythrocytes. Microscopic examination clearly revealed that most of the rabbit erythrocytes had been fumed into ghost forms.