Blood lymphocytes and lymph nodes from three patients with acquired immunodeficiency syndrome (AIDS) and two cases with AIDS-related complex (ARC) were studied during the course of the disease. The lymph node histomorphology could be grossly categorized into three stages: follicle hyperplasia, follicle degeneration and the depleted stage. In the first stage, follicles show large and sometimes irregular-sized germinal centres and narrow B-cell mantles. Dendritic reticulum cells in the germinal centres reveal disruption of their fine dendritic processes; often indentations are visible, filled with small B- and T-lymphocytes of follicle mantle and paracortical origin. These lesions may be the first signs of follicle degeneration, in which only hyalinized remnants of follicle centres are found. The changes in the paracortex are less prominent than those in the follicles. The disturbance in the numerical balance of T-cell subsets of helper-induced and suppressor-cytotoxic phenotypes is less than that found in the blood. In some cases the paracortex reveals a high density of T6-positive elements resembling interdigitating cells, suggestive of continuous antigen exposure. We found follicle hyperplasia in ARC, follicle degeneration in one case of ARC and in full-blown AIDS, while the depleted stage was found in lymph nodes at autopsy of AIDS patients. Lymph node changes do not completely correlate with the changes in the blood lymphocyte pool. Investigations on lymph nodes may be of value in the assessment of the prognosis of the disease.