The distribution of the histocompatibility antigens responsible for positive antiglobulin consumption reactions have been studied along with some of the antigens' characteristics. These antigens are present in highest concentration in liver, with kidney being second, muscle and brain third. Little if any were found in spleen and lymph nodes, and none in endocrine tissue. The antigens were found to be rendered nonreactive by lyophilization, repeated freezing and thawing, and heat of 56C for 45 minutes.