We have studied 72 cases of multiple myeloma (MM) bone marrow trephine biopsies using the monoclonal antibody PC-10 and the colloid silver nitrate method for identification of proliferating cell nuclear antigen (PCNA) and nucleolar organizer regions (NORs), respectively. PC-10 and AgNOR scores were statistically significantly different between low versus intermediate and low versus high grade of malignancy (P < 0.001), whereas their difference was not significant between intermediate and high grade. A strong correlation was identified between these two proliferation-associated indices in each histological grade. There is evidence that the proliferative state of myelomas belonging to the intermediate grade is approximately the same as that observed in high grade (blastic) ones.