Gallium-67 single photon emission computerized tomography (Ga-67 SPECT) was performed in 13 chronic lymphocytic leukaemia (CLL) patients suspected of evolution into diffuse large B-cell lymphoma (DLCL) or Richter's syndrome (RS). Six positive and nine negative Ga-67 SPECTs were observed. Ten patients were biopsied (five in each group). DLCL was not detected in any Ga-67-positive patient, including those in whom Ga-67-positive areas were biopsied. The only case of DLCL was demonstrated in a Ga-67-negative patient. The tumoral proliferative index (Ki67 antigen expression) was moderate and similar in both groups of patients. These results illustrate the limitations of Ga-67 SPECT in identifying RS.