Activated immunoglobulin which is useful as an eosinophilia-suppressing agent, immunomodulating agent, therapeutic agent for autoimmune diseases, anfiinflammatory agent and antiallergic agent is obtained by admixing immunoglobulin with a histamine component and then substantially or completely removing the histamine component. The histamine component may be removed or separated by dialysis, gel filtration, adsorption chromatography, ion exchange chromatography, or affinity chromatography. The method imparts pharmacological activity which is not inherently available in immunoglobulin of the natural type to immunoglobulin. The activated immunoglobulin of the present invention has an immunomodulating action which is clearly different from that of conventional immunosuppressive agents. It is useful as a therapeutic agent for autoimmune diseases such as chronic rheumatoid arthritis, systemic lupus erythematodes and multiple sclerosis as well as for various immunodeficiency syndromes wherein the immune system is not functioning properly. The activated immunoglobulin of the present invention may be also used as a pharmaceutical agent for eosinophilia caused by infectious diseases, parasitic diseases, diseases of respiratory organs, autoimmune diseases, malignant tumors, etc. In addition, the product of the invention may be used as an excellent antiinflammatory agent and antiallergic agent, and so is highly useful as a pharmaceutical.