The distribution of Ca2+ and Na+ conductances on neuronal precursor cells was investigated during differentiation. Ionic conductances on the soma or on the growth cone were isolated by superfusing all other parts of the cells with sucrose. Conductances on the neuritic shaft were detected as additional conductances after removing sucrose from the neuritis shaft. Neuronal precursor cells were isolated from chick dorsal root ganglia by selectively killing differentiated neurons. Cultured precursor cells differentiated into morphological and functional mature neurons. Functionally undifferentiated precursor cells (during the first 10 hr in culture) expressed only low-voltage- activated (LVA) Ca2+ currents. High-voltage-activated (HVA) Ca2+ and Na+ currents appeared delayed after more than 10 hr in culture. Voltage- dependent conductances, if expressed by a cell, were present on all parts of the surface membrane at all stages of differentiation. LVA Ca2+ conductances were well represented on the growth cone as well as on the soma in functionally undifferentiated precursor cells. During differentiation of precursor cells, LVA Ca2+ and HVA Ca2+ as well as Na+ conductances were expressed on the somatic membrane, on the neuritic shaft, and on the growth cone. These results demonstrate the expression of Ca2+ channels on growth cones during differentiation.