Recently there has been much interest in using immunohistology with monoclonal antibodies (MABs) against different cells of the immune system in lymph nodes (LNs) of patients with HIV infection. The panel of these MABs is becoming increasingly extensive. In this study we report on our finding that by using a limited number of properly chosen MABs, diagnostically and prognostically relevant parameters can be acquired. One hundred and twenty-one LN biopsy specimens from patients with HIV infection were reviewed and classified according to our expanded working classification and a fifth main type of LN lesion, the small lymphocyte follicular type, was added to our earlier classification. We propose that this new type represents a transitional form between the mixed follicular type and the follicular depleted type. In the follicular type of LN lesion there is no marked change in the number of CD4 cells within the follicles and in the extrafollicular parenchyma. The reaction against the major core proteins of HIV is always positive and the number of proliferating cells is very high. The positivity is weaker in the earlier cases and stronger in the older ones. The follicular dendritic cell (FDC) network shows degenerative changes. In the hypervascular follicular type the reaction pattern with these selected MABs is very similar to the one in the follicular type. In the mixed type there are hyperplastic follicles and regressively transformed follicles in the same node. The hyperplastic follicles show a pattern similar to those in the follicular type. However, the reaction with MABs against core proteins of HIV is often markedly stronger. The number of proliferating cells is decreased markedly. Some follicles show extensive FDC network destruction. CD4 cells within the follicles and in the extrafollicular parenchyma are decreased. The regressively transformed follicles contain very few proliferating cells and the reaction with MABs against core proteins is variable, being strong in some follicles and weak in others. The small lymphocyte type contains follicles consisting mainly of small lymphocytes. These lymphocytes are of the same phenotype as those in the primary follicles. In contrast to these, however, the numbers of CD4 and Leu 7+ cells are much decreased. The reaction with MABs to core proteins is weak and limited to the germinal centres (GCs). The number of proliferating cells is strongly diminished. The FDC network, however, is well developed in most follicles. In the follicular depleted LNs there are no follicles; however, in some LNs remnants of FDC can be seen.