A possible important role of interleukin (IL)-16 has been suggested in the development of certain autoimmune and atopic diseases, such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), atopic asthma, and atopic dermatitis.  Recent studies have revealed that the biological activities and sources of IL-16 are more varied than was previously realized.  With the progress of studies on IL-16, it is becoming apparent that this cytokine has complex role in these diseases, probably because of its multiple actions, including induction of the migration or activation and anergy (a weak or absent response to antigen-specific or nonspecific stimuli) of CD4+ cells.  In addition, certain recent evidence has indicated an antiinflammatory (but not proinflammatory) effect of IL-16 in RA.  This cytokine may also suppress inflammatory or autoimmune phenomena in other disorders.  Because of multiplicity of its actions, further characterization appears to be required to clarify the role of IL-16 in autoimmune and/or atopic diseases.