We concluded a study on 208 cases of non-Hodgkin's lymphoma and 401 controls in the North-East of Italy in order to investigate the role of indicators of socio-economic status, personal habits, past history of various disorders and medical treatments potentially affecting the immune system, and occupational exposures in the aetiology of such neoplasia. None of the several investigated characteristics appeared to be a strong determinant, i.e. relative risk, RR greater than 2.0, of non-Hodgkin's lymphoma. Cases and controls appeared to be very similar as regards education, main life-time occupation and alcohol consumption. Positive associations, however, emerged with chronic infectious diseases, mainly tuberculosis and malaria (RR = 1.8, 95% confidence interval, CI: 1.1-2.9). Non significantly increased risks were also found for smoking habit (RR ever vs never smokers = 1.5, 95% CI: 1.0-2.3), episodes of herpes zoster infection (RR = 1.4; 95% CI: 0.7-2.6) and occupation in chemical and petrochemical industries (RR = 1.6; 95% CI: 0.9-3.1, and 1.8; 95% CI: 0.9-3.8, respectively). Conversely, farming as well as specific exposure to herbicides and pesticides did not seem to affect the risk of non-Hodgkin's lymphoma in the present investigation.