Abstract
A very close serological relationship was found between CVB and PVS, while only a distant relationship was shown between CVB and CLV. Each of these viruses had its own characteristic major "antigenic fraction", distinguishing it from the others, and small "antigenic fraction" common to all four. The antiserum to CLV was shown to be the richest in various antigenic fractions, antisera against PVM and PVS had the same number of fractions but of different specificity and CVB-antiserum had the relatively smallest number of fractions.