A form of idiopathic CD4 lymphocytopenia (ICL) has been recently described. Its diagnostic criteria have been defined by the Centers for Disease Control (CDC), Atlanta. Associations of ICL with hepatitis C infection have been reported, while some ICL patients have presented abnormalities partly similar to those observed in common variable immunodeficiency (CVI). This paper illustrates the immunological pictures of two subjects with a CD4 deficiency confirmed in a series of peripheral blood lymphocyte subset determinations, but not associated with other cellular or humoral immunity abnormalities and accompanied by poorly significant clinical manifestations (no opportunistic infections). Patient one has been observed for a very long period. Her serological picture has been negative and she is free from hypergammaglobulinemia. HIV infection can thus be ruled out. Patient two has not required any specific treatment so far. The CDC's diagnostic criteria for ICL are not fully met in the two cases. Their pictures meet many, though not all of the CDC criteria for the diagnosis of ICL. It is to be hoped that a protracted follow-up will allow an assessment to be made of the natural history of the two cases.