ABSTRACT INTRODUCTION A BIOLOGICAL technique, which results in a quantitative measure, highly correlated with the relationship coefficient between individuals, has long been sought. Such technique would be of value in checking calculated relationship coefficients within lines under various inbreeding and selection schemes and for investigating the value of genetic diversity in predicting the amount of heterosis which may be obtained from specific crosses. Loeb and Wright (1927) employing histological observations demonstrated a definite association between the degree of reaction shown by the host to a skin graft and the host’s relationship to the donor. Other workers have suggested alternate methods for measuring this reaction, viz. the cellular infiltration of the graft, Loeb (1944); persistence of the graft, Billingham and Medawar (1951; and the change in the number of leucocytes and the percentage of lymphocytes in the circulating blood, Blumenthal (1939). Craig and Hirsch (1957) working with chickens, found a significant correlation . . .