A new monoclonal antibody, MEBL-1, which specifically melanocytes and their precursors, was used to examine differentiation of neural crest cells into melanocytes positive precursors of melanocytes in the trunk were mesenchyme located above the neural tube at the level stage 19, when active migration of neural crest cells route was almost complete. DiO-labelled neural crest to emigrate from the neural tube at stages 17–18 and the dorsolateral route, were found to become MEBL-1- indicates that MEBL-1 antigens are expressed by neural immediately following their emigration and neural melanogenic. Expression of the MEBL-1 antigens was in, and finally the loss of, HNK-1 antigen expression. level, MEBL-1-positive precursors of melanocytes were mesenchyme located above the dorsal side of the tube at stage 16. At the vagal level, the precursors in mesenchyme located above the dorsal side of the neural tube at stage 18. MEBL-1 reacted with the cell premelanosome-like granules in addition to the nuclear endoplasmic reticulum and Golgi apparatus of the The antigens recognized by MEBL-1 were proteins with masses of 135×103 and 115×103. We suggest that MEBL-1 earliest marker for melanogenic neural crest cells.