In the vertebrate embryo, Schwann cells lining the peripheral nerves originate from the neural crest (NC), a structure that also gives rise to ganglion satellite cells, most of the neurons of the peripheral nervous system, melanocytes, and part of the cranial mesenchyme. We have studied the emergence of the Schwann cell lineage in vitro in clonal cultures of quail mesencephalic NC cells by using the Schwann cell myelin protein antigen as an early and specific marker for myelinating and nonmyelinating cells. After 13-16 days in culture, numerous clones contained Schwann cell myelin protein-positive cells, sometimes isolated and sometimes associated with other NC-derived cell types. Detailed phenotypic analysis of the clones allowed us to infer the presence of differently committed Schwann-cell ancestors in the NC during the migration stage. In particular, we found evidence for the existence of a bipotent precursor of Schwann cells and nonneuronal satellite cells; a common precursor of neurons, satellite cells, and Schwann cells; and a pluripotent precursor of Schwann cells, satellite cells, neurons, and melanocytes. These founder cell types coexist in the NC with a committed Schwann cell progenitor of high-proliferative potential that differentiates in vitro in the absence of other peripheral cells and axons.