Five hundred and seven random bred New Hampshire chicks, the progeny of 15 sires each mated to 3 dams, were used in the study. The per cent gamma globulin levels obtained, 12.38%, 10.92%, 11.47%, 14.24% and 15.37% at hatch, 1, 3, 5 and 7 weeks of age respectively, followed a trend consistent with the literature. The drop from hatch to 1 week of age (12.38% to 10.92%) was attributed to the loss of maternal antibody coupled with a corresponding low rate of synthesis by the chick. From 1 to 7 weeks of age the per cent gamma globulin level increased although the values at 1 and 3 weeks were not significantly different. The relatively large increment from 3 to 5 weeks of age (11.47% to 14.24%) was consistent with a report in the literature. The within variance component obtained from the analyses of variance on the data of each age group considerably increased from 1 to 7 weeks of age. The sire and dam variance components showed no consistent trend, only a week to week variation. A considerable maternal affect at hatch was suggested by the sire (h2/s = -0.33) and dam (h2/d = 1.53) estimates of heritability. The analysis of variance on the combined data from 1 to 7 weeks of age resulted in a sire estimate of heritability (h2/s) of 0.26 and a dam estimate (h2/d) of 0.67. It was concluded that the additive genetic contribution accounts for 26% of the variation in the per cent gamma globulin level up to 7 weeks of age. The estimates also indicated that a maternal affect was still present at 1 weeks of age. Heritability estimates, 1 .23, 1 .02, -0.47 and -0.54 for the periods hatch to 1, 1 to 3, 3 to 5 and 5 to 7 weeks of age respectively, on the index of gamma globulin change revealed that there was a significant genetic contribution to this trait in the early periods. Regression analyses showed that the 5 to 7 week period accounted for more of the variability in 1 week per cent gamma globulin level than any other period. The importance of the 5 to 7 week period was discussed as an indicator of the environmental influence on the per cent gamma globulin at this age period. No correlation was found between growth rate and the per cent gamma globulin level up to 7 weeks of age. / Land and Food Systems, Faculty of / Graduate