Low-grade non-Hodgkin lymphomas (NHL) constitute a group of tumours with an often long survival time but, at present, with little--or no--chance of cure if the disease is not strictly local. In primarily asymptomatic patients, treatment may either be started immediately after diagnosis or deferred until symptoms occur. The possibility of predicting the symptom-free time was investigated in 64 non-selected initially asymptomatic patients with advanced low grade NHL, all of whom had treatment deferred until symptoms occurred. The most powerful predictor was the histopathological subgroup. Lymphocytic (LC) and follicular centroblastic-centrocytic (fCBCC) lymphomas had a median symptom-free period of 2 years, which was four times longer than that for immunocytoma (IC) and follicular and diffuse CBCC (fdCBCC). In addition, the serum levels of deoxythymidine kinase (S-TK) and lactic dehydrogenase (S-LDH) could predict the symptom-free period. This did not apply to S-Haptoglobin, S-Orosomucoid or stage. In a multivariate analysis, only S-TK gave additional information to histopathology. The only variable that predicted the overall survival time was the length of the symptom-free period.