A case of Burkitt-type lymphoma treated by accelerated hyperfractionated irradiation combined with the COP chemotherapy is presented. The effectiveness of treatment was evaluated on the basis of the growth curve and the radiobiological aspects are discussed. During the treatment, the initial volume doubling time (Td) of 15 days was shortened to 4.5 days suggesting accelerated tumor growth. From dose response curve estimated for clinical data taken from literature, an effDo of 1.37 Gy was calculated. Surviving fraction after 58 Gy given in the twice-a-day regimen (b. i. d.) was 10(-19) suggesting local tumor control. However, only partial remission was observed. This nonradical effect may likely result in accelerated repopulation of surviving tumor clonogenic cells. This suggests that such a fast growing tumor as Burkitt-type lymphoma (Tpot = 1 day) should be irradiated using three instead two fractions per day combined with adjuvant or concomitant chemotherapy with a short intervals between cycles.