We explanted fragments of embryonic chick dorsal root ganglia on to polylysine coated glass and cultured them in a medium containing one unit of nerve growth factor plus enough methylcellulose to give viscosities from 0.01-3,000 poise. We allowed them to grow out in the absence of a field, and then selected explants with halos of neurites which were relatively dense, relatively symmetrical, and practically free of glial cells. These selected explants were then exposed to electrical fields of up to 140 mV/mm for some hours. In media with viscosities of one poise or less, the field some times dragged the central cell mass of an explant towards the anode. However, in cases where the central cell mass did not move, fields of 70-140 mV/mm induced that sector of each neurite halo which faced the cathode to grow out several times faster than the one facing the anode.