The allergenicity of egg yolk immunoglob ulin (IgY) was studied using passive cutaneous anaphy laxis. It was observed that the intact yolk, water soluble fraction of the yolk, whole IgY molecule or its antigen binding (Fab9 ) and crystallizable (pFc9 ) fragments produced by pepsin digestion, elicited low IgE antibody response in mice when com pared to egg white, a known allergen. The pFc9 fragment of IgY was more antigenic than the Fab9 fragment as determined by ELISA. Low cross-reactivity was also observed between the egg yolk proteins and egg white antibodies. The low IgE antibod y response to the egg yolk proteins was associated with a higher suppressor T-lymphocytes or lower helper T-lymphocytes, or both, in comparison to egg white derived lymphocytes.