While cell suspension immunophenotypic studies are widely used as an aid in the diagnosis and classification of lymphomas and leukemias, much less attention has been directed toward interpretation of the results in reactive lymphoid proliferations. Cell suspension immunophenotypic data were therefore analyzed for 119 lymph nodes with reactive lymphoid proliferations which were divided into five major histologic categories: follicular hyperplasia, marked (FH,M), or moderate (FH); dermatopathic lymphadenopathy (DL); diffuse hyperplasia (DH); or "other." With the aid of a computer-assisted morphometer, the following were also measured and calculated: proportion of node occupied by follicles, mean relative follicle size, and mean follicle shape factor. Finally, in 57 cases, the influence of human immunodeficiency (HIV) status on the findings was analyzed. Although individual cases varied widely, cases of DL had significantly more CD3+ (T) cells, higher CD4:CD8 ratios, and fewer CD19+ (B) cells than other categories. Cases of FH,M had significantly lower CD4:CD8 ratios and more CD19+, CD10+, and transferrin receptor positive cells. Cases of FH,M and FH known to be HIV-negative had higher CD4:CD8 ratios than the HIV-positive cases. Peripheral blood CD4:CD8 ratios performed in 38 patients showed a strong correlation with nodal ratios. Morphometric data supported the correlation between follicular hyperplasia and increased proportions of CD19+, CD10+, and transferrin receptor-positive cells. Rare cases had CD5:CD2 or CD3 ratios of greater than 1 or "monoclonal" kappa to lambda ratios. CD4:CD8 ratios varied widely, but aberrant T cell phenotypes were not identified. These studies demonstrate that, although great variation exists, there are certain associations between types of reactive lymphoid hyperplasia and cell suspension immunophenotypic findings.(ABSTRACT TRUNCATED AT 250 WORDS)