SummaryTwo new erythrocyte antigens have been detected by isoimmune antibodies obtained from Gottingen Miniature pigs. By family studies they proved to belong to the E system. The factor designated En is genetically controlled by allelesE2=Eedghkmn,E3=Eaegln,E4=Eedfhkmn,E6=Eaefln,E9=Eedghjmn,E12=EaegmnoandEedgkln, and the factor designated Eo by the alleleE12=Eaegmno.The En blood factor occurs in all the breeds studied and in frequency it comes close to a related Ee factor. It stands in opposition not only to Eb but also to Ei factor. The Eo factor can be characterized as a rarely occurring Ea subgroup. Besides being antithetic to Ed it is also antithetic to El and Ei factors. For the present, it was found only in Miniature pigs.