Cell kinetics ([3H]-thymidine labelling index, [3H]-Thy LI) were determined on pathologic lymph nodes from 175 untreated adult patients. [3H]-Thy LI significantly differed in low-grade and high-grade malignancy groups according to the Kiel classification (median values, 1.8 per cent and 10.4 per cent, respectively) and in low, intermediate, high grade according to the Working Formulation (median values: 1.7 per cent, 4.8 per cent and 14.2 per cent, respectively) but was unrelated to pathologic stage or patient's age. Cell kinetics, histopathology, pathologic stage and patient's age were significant discriminants of 6-year survival. Multivariate analysis was performed by Cox's proportional hazard model to investigate the role of [3H]-Thy LI after making allowance for the other prognostic factors. When [3H]-Thy LI was added to the model, a large increase (chi square = 29.94) contributed by the cell kinetic variable in identifying patients at different risk was revealed.