1. Four additional families illustrating the clinical and genetic relationships of Cooley’s anemia and Cooley’s trait have been presented.

2. Blood findings in an offspring of a patient with Cooley’s anemia are recorded.

3. The asymptomatic nature of Cooley’s trait and its differentiation from Cooley’s anemia has been emphasized.

4. The inheritance of Cooley’s trait and Cooley’s anemia may be best explained in terms of an incomplete dominant or of the simultaneous appearance of two nonallelomorphic genes.

ACKNOWLEDGMENT We are indebted to Dr. John H. Linner for many of the observations on the Ca family and to Miss Clara Gillette for observations on the Cr family.