Abstract 1. 1.|Human erythrocyte membranes (ghosts) were treated with four non-ionic detergents at pH 9.2 (5 °C) in a dilute buffer. More than 85% of the protein was solubilized. A protein concentration of up to 4 mg/ml was obtained. 2. 2.|The solubilized proteins were examined with rabbit antibodies against membrane material by crossed immunoelectrophoresis in agarose gels containing the solubilizing detergent. 3. 3.|The immunoelectrophoretic analyses showed that the membrane proteins were stable at −196 °C in the intact membrane. After solubilization with a non-ionic detergent changes occurred within two days at 5 °C but not at −20 °C. 4. 4.|A total of 19 membrane-specific immunoprecipitates were observed by crossed immunoelectrophoresis in the non-ionic detergent Berol EMU-043. Similar precipitation patterns were obtained with other non-ionic detergents. Some of the immunoprecipitates formed two peaks and some showed reaction of partial identity. 5. 5.|The antibodies precipitated most of the solubilized protein as demonstrated by immunoabsorption in an agarose gel of electrophoretically migrating antigens. 6. 6.|The precipitation pattern in crossed immunoelectrophoresis with a given antibody solution was reproducible with different membrane preparations. 7. 7.|Crossed immunoelectrophoresis in non-ionic detergents can be used for analysis of membrane protein fractions as a complement to polyacrylamide gel electrophoresis in dodecylsulfate.