Humoral immunity involves molecules in solution in biological fluids including effectors of non specific immunity (e.g. complement, cytokines) and specific immunity (antibodies) as well. Acquired humoral immunodeficiences are often multifactorial in origin and associated with defects of cell-mediated immunity. The most common etiologies are those of iatrogenic immunodeficiencies: surgery (especially splenectomy), radiotherapy, chemotherapy of leukemia and cancer, immunosuppressive treatments in organ transplanted patients. Protein-caloric malnutrition also induces cellular and humoral immunodeficiencies. Among other causes, three types of diseases may induce defective antibody production: 1/B cell neoplasias (e.g. multiple myeloma, chronic lymphocytic leukemia...) 2/renal diseases (nephrotic syndrome, renal insufficiency) and 3/various infectious diseases, including AIDS. Some principles of prevention and treatment of secondary humoral immunodeficiencies are given.