ABSTRACTAdult brown shrimp (Penaeus aztecus) maintained in the aquatic animal medicine laboratory, were challenged with a field isolate of Vibrio anguillarum. One tenth cc of a 24‐hr broth culture diluted 100‐fold was introduced beneath the dorsal carapace at the terminus of the rostral groove. At daily intervals afterwards, hemolymph was withdrawn, smears prepared and indirect fluorescent antibody and immunoelectrophoretic measurements performed. The shrimp were processed to detect presence of organisms within tissues by the direct fluorescent antibody technique. The studies indicated that an electrophoretic component which migrates similar to vertebrate beta lipoprotein emerges 48 hrs after challenge. Phagocytic activity was apparent, and bacteria tended to concentrate in the hepatopancreas gland. The significance of these preliminary observations lie in the appearance of a unique electrophoretic component in shrimp hemolymph which may be of some value in assessing the shrimps disease status, and the location of a site in which V. anguillarum, and possibly other disease producing bacteria, are concentrated during infection.