Immunoglobulin D preparations isolated from three different myeloma sera failed to elicit reversed passive cutaneous anaphylaxis reactions in guinea pigs. Although the proteins aggregated readily with bisdiazotized benzidine, the aggregates did not fix complement and caused no increase in the vascular permeability of guinea pig skin. Under identical conditions human IgG preparations gave positive reactions in all tests. It is concluded that immunoglobulin D, both in its native and aggregated forms, lacks the structural features necessaru for skin binding and complement fixation. © 1969.