A histopathological survey of wild blue shrimp Penaeus stylirostris from the Gulf of California, Sonora, Mexico, revealed the presence of infectious hypodermal and hematopoietic necrosis virus (IHHNV). The survey performed at 39 sampling stations during August-September 1990, showed the prevalence of IHHNV infection to be 46% in the upper Gulf zone and 26% in the central-lower Gulf zone. The presence of IHHN virus was confirmed with the IHHNV-specific gene probe BA401 by means of in situ hybridization. Specimens of the Pacific brown shrimp P. californiensis (also known as yellowleg shrimp) and Pacific white shrimp P. vannamei, incidentally captured during the survey, were also analyzed and found to be infected by IHHNV. The survey demonstrated that IHHNV had widespread distribution in a region where it had not been previously detected and, presumably, was not present before 1987. These findings suggest that IHHNV has become established in wild populations of P. stylirostris, and perhaps in P. californiensis and P. vannamei, in the Gulf of California.