The Kiel classification provides a new subdivision of non-Hodgkin lymphomas into distinct entities showing different clinical and prognostic properties. In comparison with earlier classifications this system defines additional types of lymphoma (e.g. CC lymphoma, LP immunocytoma) (for abbreviations see text) which are to be considered separate entities also from a clinical point of view. By data derived from a multicenter prospective observation study (1,127 patients recruited from 1975 to 1980, follow-up until 1985) a precise definition of the clinical features of each lymphoma entity (e.g. frequency, age and sex distribution, patterns of initial involvement and spread of disease) was possible. In addition, the effect of radio- and/or chemotherapeutic measures was evaluated. Strictly localized disease (stage I/IE according to the Ann Arbor classification) occurred in 1.5 to 8% of patients with NHL of low-grade malignancy (comprising 69.4% of cases studied) and in 8 to 17% of patients with high-grade malignant NHL (comprising 30.2% of cases studied). Loco-regional irradiation alone was able to induce complete remission in 86 to 89% (CB and IB lymphomas) and in 100% (LP immunocytoma, CB-CC and CC lymphomas), respectively, of stage I/IE patients. Only CC and IB lymphomas showed a relevant risk of relapse (40% and 50%, respectively). Total lymphoid irradiation as able to induce stable complete remissions in about 50% of patients with stage III of CB-CC lymphoma. Probabilities of survival of patients with initial stages III and IV treated by several types of chemotherapy reflect different prognostic features of individual lymphoma entities.(ABSTRACT TRUNCATED AT 250 WORDS)