Anti -- A and anti -- B activities were determined in fractions from the sera of group A, group B or group O donors by the following tube agglutination methods. One drop of each sample was added to one drop of a 2% suspension of group ** f or group B red cells in a small ** f test tube. In several instances group O cells were also used as controls. The red cells were used within 2 days after donation and were washed with large amounts of saline before use. The mixtures of sample plus cell suspension were allowed to stand at room temperature for 1 hr. the tubes were then centrifuged at 1000 rpm for 1 min and examined macroscopically for agglutination. For the albumin method, equal volumes of 30% bovine albumin, sample and 2% cells suspended in saline were allowed to stand at room temperature for 1 hr and then were centrifuged at 1000 rpm for 1 min. All samples were tested by both the saline and albumin methods. The activities of fractions of sera containing Rh antibodies were tested by the saline, albumin and indirect Coombs techniques. Homozygous and heterozygous ** f cells, ** f and homozygous and heterozygous ** f cells were used to test each sample; however, in the interest of clarity and conciseness only the results obtained with homozygous ** f and homozygous ** f cells will be presented here.

The saline and albumin tests were performed as described for the ABO samples except that the mixture was incubated for 1 hr at 37 ` C before centrifugation. The saline tubes were saved and used for the indirect Coombs test in the following manner. The cells were washed three times with saline, anti human serum was added, the cells were resuspended, and the mixture was centrifuged at 1000 rpm for 1 min and examined for agglutination. The anti human sera used were prepared by injecting whole human serum into rabbits. Those antisera shown by immunoelectrophoresis to be of the ``broad spectrum'' type were selected for used in the present study.