Lymph node biopsies from 16 cases of intravenous drug addicts with lymphadenopathy syndrome (LAS) have been examined at the electron microscope. The main ultrastructural alterations observed in the lymphocytes, dendritic reticulum cells and endothelial cells were tubulo-reticular structures (TRS), test tube and ring shaped forms (TRF) and nuclear pockets (NP). Images suggesting virus budding from lymphocytes and virus-like particles have also been found in 9 out of the 16 cases. The possibility to correlate the latter findings with a better knowledge of LAS evolution and prognosis is discussed.