In most cases of centroblastic/centrocytic follicular lymphomas the bcl-2 proto-oncogene (18q21) is translocated to the immunoglobulin JH region of chromosome 14 (14q32). About three quarters of the translocations are concentrated on the 3' nontranslated, a few hundred basepare-long region of bcl-2, the so called major breakpoint region (mbr), the remaining 20-25% is located about 30 kilobases downstream of bcl-2 coding sequences in the minor cluster region (mcr). The majority of the immunoglobulin breakpoints can be found in JH6-4 genes. The polymerase chain reaction method can detect the translocation already in a very few number of cells (> 10(3)). This very sensitive technique makes it possible to detect the translocation in lymphoid/lymphoma of peripheral blood and bone marrow that are missed by other diagnostic methods. This way one can perform a quick, early diagnosis, examine the result of treatments as well as detect the remissions and the possible relapses right at the beginning. All the advantages of this method contribute to a more successful treatment of follicular lymphoma. This present work describes a polymerase chain reaction technique which is capable of a detection of the t(14;18) translocation in a patient of centroblastic/centrocytic lymphoma, moreover shows how this translocation disappears after 4 week of radiotherapy of the patient.