T-cell proliferative responses to the mitogenic monoclonal antibody anti-Leu 4 were assessed in healthy controls, lymphadenopathy syndrome (LAS) patients, and acquired immune deficiency syndrome (AIDS) patients. While 19% of the control group showed low anti-Leu 4 responses (<12,000 cpm),="" 60%="" of="" the="" las="" patients,="" 71%="" of="" the="" aids-opportunistic="" infection="" patients,="" and="" 50%="" of="" the="" aids-kaposi''s="" sarcoma="" patients="" showed="" low="" responses.="" t-cell="" responsiveness="" in="" healthy="" low="" responders="" was="" greatly="" enhanced="" by="" the="" addition="" of="" monocytes="" from="" an="" anti-leu="" 4="" high="" responder="" (responder="" monocytes).="" we="" therefore="" sought="" to="" determine="" if="" the="" low-responder="" state="" in="" las="" and="" aids="" patients="" was="" also="" mediated="" by="" monocytes="" and,="" thus,="" correctable="" by="" the="" addition="" of="" responder="" monocytes.="" in="" the="" las="" low-responder="" group,="" the="" level="" of="" enhancement="" by="" healthy="" responder="" monocytes="" was="" similar="" to="" that="" observed="" for="" the="" healthy="" low-responder="" group.="" in="" the="" aids="" low-responder="" group,="" however,="" the="" level="" of="" enhancement="" was="" significantly="" lower="" than="" that="" observed="" in="" the="" healthy="" low-responder="" and="" las="" low-responder="" groups.="" these="" findings="" suggest="" that="" impaired="" proliferation="" to="" anti-leu="" 4="" in="" las="" patients="" may="" be="" due="" to="" a="" monocyte="" defect="" similar="" to="" the="" monocyte="" defect="" responsible="" for="" low="" anti-leu="" 4="" responses="" in="" healthy="" controls.="" aids="" patients,="" however,="" show="" additional="" defects="" in="" anti-leu="" 4-induced="" proliferation="" that="" are="" not="" fully="" corrected="" by="" the="" addition="" of="" responder="">