The ontogeny ofα-,β-, andδ-crystallin antigens in the developing lens of mallard(Anaa platyrhynchos)was investigated by indirect immunofluorescence using specific antibodies to mallardα-,β-, andδ-crystallins raised in rabbits.The IgG fraction from each antiserum was isolated by affinity chromatography usign Protein A Sepharose CL-4.B. Fluoresceine (FITC) or rhodamine (TRITC) conjugated goat anti rabbit (GAR)γ-globulin was used as the secondary antibody.The results show thatα-,β-, andδ-crystallins appear simultaneously in the developing mallard lens and are detectable from 66 hr (stage 15/16). This situation is different from the chick whereδ-is known to appear first followed byβ-, andα-. This could be due to species variation.In the epithelium, however, as in the chick,δ-emerges first followed byβ-, andα-but rather late when compared with the chick and this seems probably due to a difference in the incubation time between the two species.Results from immunofluorescence and Tris-SDS gel electrophoresis demonstrate thatαA subunit of theα-crystallin appears much earlier than theαB subunit.We also found that the newly discoveredε-crystallin (18) appears long after the three major crystallin classes.