The great diversity of arthropod body plans, together with our detailed understanding of fruit fly development, makes arthropods a premier taxon for examining the evolutionary diversification of developmental patterns and hence the diversity of extant life. Crustaceans, in particular, show a remarkable range of morphologies and provide a useful outgroup to the insects. The amphipod crustacean Parhyale hawaiensis is becoming established as a model organism for developmental studies within the arthropods. This protocol provides a simplified protocol for antibody staining of P. hawaiensis embryos. The method also works well for other arthropods and phyla. Fixed embryos are rehydrated, washed, blocked with normal goat serum, and incubated overnight with primary antibody. Embryos are then washed and incubated with a peroxidase-conjugated secondary antibody that binds to the primary antibody. A subsequent histochemical reaction produces a black stain in those cells where antibodies have localized.