Serum mucoprotein level in 16 normnls and 3CO cases of diseased was investignted by Winzler' s method. Using biuret rengent normal range of serum mucoprotein proved to be 94-120mg per cent. Higher mucoprotein content was often recognized in rheumatoid arthritis, cancer, pneumonia, and hepatitis. High mucoprotein level in cancer or ulcer patients was decrensed after their resection. A positive linear correlation wns shown between erythrocytes sedimentation rate and mucoprotein level in serum. But no close relation was observed between serum mucoprotein and Takata reaction, Wassermann reaction or total protein content in serum.