OBJECTIVE: To analyze-cellular proliferation in non-Hodgkin's lymphoma (NHL) of T-cell origin using three variables available on histologic paraffin, dewaxed sections. STUDY DESIGN: The study group consisted of 35 T NHLs (22 low and 13 high grade). Two immunohistochemical methods established the percentage of cells expressing proliferating cellular nuclear antigen (PCNA), or PCNA index, and the Ki-67 antigen, or MIB-1 index. The third method quantified nucleolar organizer regions (NORs) with an image analyzer, giving the NOR area and number of NORs; an internal reference on lymphocytes was used. RESULTS: For the PCNA index, each subtype of low grade NHL demonstrated a difference as compared with high grade NHL except for angioimmunoblastic type NHL (AILD). The difference between the two grades became significant after including AILD-type NHL within high grade NHL (P = .02). The MIB-1 index gave similar results. The PCNA index and MIB-1 correlated (r = .55, P = .008). The relative NOR area and number of NORs differed significantly between the two grades (P < 10(-4) and P < 10(-2); the absolute NOR area differed to a lesser degree (P = .02), and no difference was observed for the absolute number of NORs (P = .07), stressing the importance of an internal reference. NOR areas and numbers correlated highly (r = .90 for relative and .78 for absolute variables, P < 10(-4)). No relation was found between PCNA and MIB-1 indexes. CONCLUSION: Correlations between these variables and grades of malignancy, between the two indices with each other and between the AgNOR variables with each other, including referring to internal lymphocytes, were reported for these T NHL-like tumors in studies on B NHL. The proliferative character of the AILD-type T NHL was in accordance with their worse prognosis. The absence of a correlation between PCNA or MIB-1 indices and NOR variables may reflect a biologic difference between B and T NHLs in a shorter cell cycle or more important functional activity in T NHL.