Cell electrophoresis allows separation of normal human blood lymphocytes into two main groups which are a function of their relative rates of migration, with regard to the reference speed (1 mum.sec.-1V-1.cm): the lymphocytes which have a greater mobility than this value seem to be T-lymphocytes (80,1 per cent for 42 healthy adults); on the contrary, B-lymphocytes have an inferior mobility (19,9 per cent). Two known methods are used for the selection of the lymphoid populations: spontaneous rosetting with sheep's red blood cells, which are characteristic of T lymphocytes, and adherence to nylon wool columns, which is dominant in the case of B-lymphocytes. This method confirms the fact that T-lymphocytes have a rapid migration and B-lymphocytes a slow migration. We have isolated a third population, having neither the T markers, nor the B markers. It has a very homogeneous migration, centered on the two classes 1,05 and 1,10 mum.sec.-1.V.-1.cm.