An analysis of the modes of distribution of initial sites of involvement in patients with Stage II and III non-Hodgkin's lymphoma revealed a contiguous pattern of involvement of lymph node bearing areas directly connected by lymphatic channels in 76% of patients with nodular lymphomata and in 84% of those with diffuse lymphomata. The patterns and frequencies of initial relapse following radiotherapy for each histopathological type and stage (Stage I-III) are described. The sites of relapse are analysed in relation to initial pretreatment sites of involvement and in relation to radiation fields employed. The therapeutic implications of these data are discussed.