Los “anticuerpos naturales” del suero, en Bovinos Criollos, orientan otra pauta de los “Marcadores genéticos sanguíneos” para IDENTIFICACION Y PRESERVACION de su GERMOPLASMA. Se trabajó con dos rodeos de 82 Bovinos Criollos, aplicando la metodología siguiente: a) Extracción de muestras de sangre a cada animal por vía yugular, b) Tipificación sanguínea por el “Método hemolítico” con fijación de Complemento Fresco de Conejo, c) Especificidad de los Inmunosueros Naturales “anti-factores sanguíneos”, por “absorciones” con eritrocitos bovinos de Grupos Sanguíneos conocidos. Se detectaron anti-J anti-V, etc. Se comprueba que la producción natural de anticuerpos antifactores sanguí- neos en Bovinos, cualquiera sea su especificidad, invariablemente está asociada a la negatividad del Sistema J, considerándose, además, que no es improbable que el gene o genes vinculados a esta particularidad, pongan en juego algún mecanismo defensivo en individuos de alta resistencia en Areas Marginales. Se discute si los anticuerpos naturales representarían un nuevo tipo de Marcadores Inmunogenéticos.Serum natural antibodies in creole Cattle bear other patterns of the “blood genetic markers” for their GERMPLASM IDENTIFICATION and their corresponding PRESERVATION. We worked with several herd or Creole Cattle (Criollos) from different areas of Argentina, but this report corresponds to two herds of 82 Creole Cattle or “Criollos” from Experimental Farm of Balcarce - INTA - (Argentina) using the following methodology. a) the blood samples of each animal (sera and red cells) were collected from yugular vein, b) red cell samples from every animal were typed with 60 reagents (From Iowa State University, USA), plus some replicate and experimental Argentine reagents, plus rabbit complement (Selected rabbit sera stored fresh frozen), c) specificity of natural “anti-blood factors” isoimmunosera were determined by absorptions using bovine red cells of well-know blood groups. It was detected anti-J, anti-V, one serum that reacts as anti-M, and others not identified antibodies. The increasing number of discoveries of specific and differential blood group and histocompatibility antigens, with its corresponding natural antibodies and those produced by immunization, has enriched the knowledged of the animal genetic individuality. When it was disposable family inheritance data on this phenomenon were studied. It is discussed if natural isoantibodies of bovine normal sera would represent a new type of Immunogenetic Markers; or whether natural isoantibodies are alsoundcr the influence of associated environmental factors.Facultad de Ciencias Veterinaria