1. An example of the blood group antibody, anti-Lub, was found in a patient who had a mild hemolytic transfusion reaction. It was shown to possess the characteristics of an immune antibody and to be able to distinguish between a single dose and a double dose of the Lub gene. 2. Three new examples of the antibody, anti-Lua, are presented. All of them were found in normal blood donors and have properties which indicate that they are naturally occurring antibodies. Dr. R. R. Race and Dr. R. Sanger confirmed the presence of anti-Lub in Mrs. S.’s serum, and studied other members of her family and the three anti-Lua sera. We are grateful to them for many favors and their kind encouragement. We are obligated to Miss Marie Cutbush for making available the LuaLua cells from Mrs. R. and her sister, and for a supply of anti-Lub serum. Thanks are due to Dr. A. E. Mourant who furnished our original supply of anti-Lua serum and to Dr. Philip Levine for the anti-Tja and anti-Vel sera. We are indebted to Dr. J. M. Fine of Milwaukee for permission to study Mrs. S. and to the patient and her family for their cooperation. The sera from 18,613 blood donors were studied by Betty McCarthy, Rosemary Polka, Pearl Lemke, Agnes Molnar, Jeannette Flagstadt and Betty Hutter.