We used an Avidin-Biotin peroxidase complex (ABC) immunoperoxidase technique to evaluate the localization of IL-6 of human bone marrow cells in multiple myeloma (MM). The cellular distribution of IL-6 was determined at light and electron microscopic levels. The author's study indicated that cytoplasmic IL-6 was detected only in the myeloma cells of bone marrow cells. Immunoelectron microscopic (immuno-EM) study showed positive reactivity mainly in the perinuclear space (PNS), well-developed rough endoplasmic reticulum (RER), and Golgi area.