Lens antigens, detected by immunofluorescence using rabbit antiserum against adult chick lens, appear in the chick embryo at stage 16. When eye rudiments are cultured in vitro, antigens developed; but they did not when optic cups were cultured but for a few cases. Isolated presumptive lens ectoderm from stage 4 did not develop antigens when cultured, but such ectoderm from stages 7–9 developed lens antigens and also showed lens structures. Stage 4 ectoderm could be induced to lens antigen development by alcohol-killed optic cups from stages 9–13. The experimental system can be used for in vitro studies on lens induct