The clinical, pathological and immunological features in 5 cases of T-cell lymphoma without overt marrow involvement are described. Classification of this distinct sub-group of lymphoma on morphological and clinical criteria alone has been shown to be unreliable, and precise recognitionr equires additional information from cytochemical and immunological marker studies of peripheral blood and lymph nodes. Valuable information may also be obtained from analysis of pleural fluid. The accurate identification of this sub-group assumes new clinical relevance in the light of the considerable improvement in prognosis reported with treatment schedules that are effective in acute lymphoblastic leukaemia.