This study describes a series of immunological investigations carried out on a group of 37 HIV-seropositive children, aged 3-4 years, in two different stages of disease defined according to the CDC classification; the Primary stage, an asymptomatic one, showing abnormal immune function (P1-Class, B-Subclass) and the Secondary stage, 6-8 months later, in which patients exhibited non-specific findings, i.e., loss of weight, persistent generalized lymphadenopathy and hepatosplenomegaly, associated with abnormal immune function (P2-Class, A-Subclass). In both stages, immune function was considered 'abnormal' when lymphopenia and a decrease of the CD4/CD8-cell ratio were found. The phenotypes CD16+/56+ (NK) and HLA-DR+/CD3+ (T-activated?)-positive cells, were assessed by flow cytometry, and the following supplementary systemic humoral markers were investigated in homologus serum samples; total HIV(gp)-antibody, HIV(p24)-antibody and p24-antigen presence. If at the primary stage, no significant difference from to the reference values corresponding to the age was noticed, at the Secondary stage the obtained data is presented separately in two subgroups, namely the A-subgroup characterized by the presence of total HIV(gp)-antibody, the presence of HIV(p24)-antibody and the absence of p24-antigenaemia, and the B-subgroup, where total HIV(gp)-antibody was present, HIV(p24)-antibody absent and p24-antigenaemia present. A significant decrease of CD16+/56+ (NK)-cells was found within the two subgroups. As far as HLA-DR+ from CD(3+)-cells was concerned, only those within the B-subgroup showed a high percentage level, compared to the reference values. The importance of the present findings, linked to immune monitoring of HIV infection among children, is discussed.