The labeling index has been determined in 34 non-Hodgkin malignant lymphomas. The kinetic parameter has been analyzed in relation to the different histologic types, according to the Kiel calssification, and a kinetic classification with three main groups at low, intermediate, and high proliferative activity has been proposed. The analysis of the survival of the patients in relation to the labeling index of the malignant lymphoma cell population has shown that the potential proliferative activity has an important prognostic significance.