Previous measurements of the lateral electric fields near skin wounds in guinea pigs have detected DC fields between 100-200 mV/mm near the edge of the wound. We have studied the translocation response of motile primary human keratinocytes migrating on a collagen substrate while exposed to similar physiological DC electric fields. We find that keratinocytes migrate randomly on collagen in fields of 5 mV/mm or less, but in larger fields they migrate towards the negative pole of the field, exhibiting galvanotaxis. Since these cells have an average cell length of 50 microns, this implies that they are able to detect a voltage gradient as low as 0.5 mV along their length. This cath-odally-directed movement exhibits increased directedness with increasing field strengths between 10 and 100 mV/mm. We observe a maximally directed response at 100 mV/mm with half of the cells responding to the field within 14 minutes. The average speed of migration tended to be greater in fields above 50 mV/mm than in smaller fields. We conclude that human keratinocytes migrate towards the negative pole in DC electric fields that are of the same magnitude as measured in vivo near wounds in mammalian skin.