1. Two types of cataphoresis apparatus for determining, under aseptic conditions, the charge carried by biologically active substances, such as Bacteriophage are described. One cell depends upon the electrophoresis of particles into agar and their subsequent re-suspension in a fluid medium for testing purposes. This cell has certain advantages when employed in connection with agents of small dimensions ordinarily inactivated by prolonged exposure to required test conditions. 2. Several separate races of anti-coli Bacteriophage have been found to bear a negative charge within a range of H-ion concentrations from pH. 9.0 to pH. 3.4. At pH. 3.35 and below, the lytic particles migrate through agar to the cathode. It is likely that the reversal in direction of migration is due to the assumption of a positive charge by the Bacteriophage corpuscle.