Envelope components were separated from Venezuelan, Eastern, and Western equine encephalomyelitis viruses after treatment of the virions with detergent. Vaccines prepared from the envelope component were capable of stimulating mice to produce humoral antibodies. Protective efficacy studies were performed using mono-, di-, and trivalent vaccine combinations. These elicited varying degrees of homologous protection, and Eastern and Venezuelan equine encephalomyelitis envelope products appeared to confer protection to mice challenged with Western equine encephalomyelitis virus.