Genetic deficiency of the alpha-gamma-subunit of the eighth complement component (C8 alpha-gamma) was found in a strain of the New Zealand White rabbit. The serum of this deficient rabbit lacked the immunochemical and functional alpha-gamma-subunit of C8. Mating tests indicate that the C8 alpha-gamma deficiency is transmitted as a simple autosomal recessive trait with the following physiologic characteristics. The body weight at the first week of life, mature weight, and litter size of the deficient animals were smaller than those of heterozygous and normal ones. In addition, survival rates for the first 3 mo of life of the deficient animals tended to be lower than those of heterozygous and normal littermates.