An extract of spleens from three pheasants affected with marble spleen disease was used as an intravenous inoculum to transmit the disease to pen reared pheasants (Phasianus colchicus x Phasianus torquatus). The disease was prevented by specific convalescent pheasant antiserum and by antiserum from turkeys that had recovered from hemorrhagic enteritis of turkeys. The causative agent of the disease passed through 0.22 μ filters, resisted chloroform and retained its precipitin antigen quality after propagation by bird passage. Filterability, chloroform resistance, antigenic characteristics and in vivo response to antibody strongly indicate that the causative agent of marble spleen disease is a virus very similar to the virus which causes hemorrhagic enteritis of turkeys.