Exogenous chicken alpha-Fetoprotein (AFP) was added to embryonic chick dorsal root ganglia plated on gelatin-coated tissue culture dishes at different stages during the differentiation process and its intracellular uptake demonstrated by immunocytochemical methods. Other embryonic serum proteins were added as a control. Morphologically well-differentiated neurons (ganglion cells) appeared positively labeled for AFP, contrasting with weakly stained other cell types: these included spindle-shaped cells identified as Schwann cells and larger, often closely packed cells, which could be less mature neurons. Fibroblasts were found negative or faintly stained. No AFP was noticeable in cultures grown in the absence of the protein. These results suggest that the presence of AFP in the developing CNS is for the most part, if not entirely, due to protein uptake as opposed to in situ synthesis.