This paper describes the results of a field evaluation of a novel M. hyo bacterin, Ingelvac MycoFLEX (Boehringer Ingelheim Vetmedica, Inc., St. Joseph, Mo.), and another commercially available vaccine in a conventional production system positive for PRRSv, Salmonella typhimurium, Lawsonia intracellularis and SIV and Mycoplasma hyopneumoniae (M. hyo).