A technique of microinjection of exogenic commercial lactate dehydrogenase into the zygotes of rats has been elaborated. A selective inhibition of exogenous LDH-3, LDH-4 and LDH-5 was registered in the ova-recipients. Attempts to reproduce the selective inhibition of LDH-3, LDH-4 and LDH-5 by a microhomogenate made of zygotes were not successful. The identification of LDH from ovocytes and exogenic LDH was made according to their electrophoretic mobility relative to Bromphenol blue and LDH-1.