Opsonic glycoprotein, alpha 2-HS-glycoprotein concentration was studied in the serum of 753 patients with various hematological, malignant, immunological, metabolic, endocrine and liver diseases and 68 healthy controls. Decreased serum alpha 2-HS-glycoprotein levels were detected in patients with acute leukemias, chronic granulocyte and myelomonocyte leukemias, lymphomas, myelofibrosis, multiple myeloma, metastatizing solid tumors, systemic lupus erythematosus, rheumatoid arthritis, acute alcoholic hepatitis, fatty liver, chronic active hepatitis, liver cirrhosis, acute and chronic pancreatitis, and Crohn's disease. Elevated levels were measured in patients with B and NANB/C hepatitis. Further decreased levels were observed in some groups with secondary infections. Serum alpha 2-HS-glycoprotein levels are affected by many factors, influencing the synthesis and elimination of the protein. The detection of serum alpha 2-HS-glycoprotein concentration has no specific diagnostic value as a marker for tumors or other diseases, however, its determination can be useful for the assessment of a non-specific regulator of the host defence.