WE demonstrate that widespread programmed cell death exists in proliferative regions of chicken optic tectum during early development using a sensitive fluorescent ISEL method (FISEL+) and antibody staining for an antigen in dying cells. Several developmental stages from embryonic day (E) 3 to E18 were examined. FISEL+- positive cells were rare before E7 and between E9 to E12. However massive labeling was observed in the ventricular zone (VZ) between stages E7.5 and E8. At this time extensive cellmigration is underway and many labeled cells were found not only in the VZ (premigratory cells) but also in the intermediate zone and tectal plate (migra-tory cells). Many labeled cells were also found in upper tectal laminae at late developmental stages (E15 and E18).