Enteric neurons and glia arise from the neural crest. The phenotype of crest-derived cells was examined as they differentiated into neurons or glia in the mouse small and large intestine. Previous studies have shown that undifferentiated enteric crest–derived cells are Phox2b+/Ret+/p75+/Sox10+, and at embryonic day (E) 10.5, about 10–15% of the crest-derived cells in the small intestine have started to differentiate into neurons. In the current study, by E12.5 and E14.5, about 25% and 47%, respectively, of Phox2b+ cells in the small intestine were immunoreactive to the pan-neuronal protein, ubitquitin hydrolase (PGP9.5), and the percentage did not change dramatically from E14.5 onward. The differentiation of crest-derived cells into neurons in the colon lagged behind that in the small intestine by several days. Differentiating enteric neurons showed high Ret, low p75, and undetectable Sox10 immunostaining. Glial precursors were identified by the presence of brain-specific fatty acid binding protein (B-FABP) and detected first in the fore- and rostral midgut at E11.5. Glial precursors appeared to be B-FABP+/Sox10+/p75+ but showed low Ret immunostaining. S100b was not detected until E14.5. Adult glial cells were B-FABP+/Sox10+/p75+/S100b+. A nucleic acid stain (to identify all ganglion cells) was combined with immunostaining for PGP9.5 and S100b to detect neurons and glial cells, respectively, in the postnatal intestine. At postnatal day 0, fewer than 5% and 10% of cells in myenteric ganglia of the small and large intestine, respectively, were neither PGP9.5+ nor S100b+. Because some classes of neurons are not present in significant numbers until after birth, the expression of PGP9.5 by developing enteric neurons appeared to precede the expression of neuron type–specific markers. J. Comp. Neurol. 456:1–11, 2003. © 2002 Wiley-Liss, Inc.