Eight cases of myelosarcoma without acute leukaemia at time of diagnosis were reviewed and biopsies were immunostained using antibodies reacting with myeloid/monocytic markers. Initial tumour location included lymph nodes, paranasal sinuses, nasopharyngeal and/or orbital regions and other extranodal locations. Three cases developed acute myeloblastic leukaemia within 1-9 months. Diagnosis was correct in four of the cases, in the other cases a non-Hodgkin's lymphoma was initially diagnosed. Morphological examination showed a blastic but variable appearance of the tumours. In a few cases cytoplasmic granulation was present. Chloroacetate esterase was present in all cases. In paraffin sections cathepsin G. elastase or lysozyme were present in all cases except one. In frozen material from four of the cases, the myeloid markers CD 11c and CD 33 were present (all cases) and CD 13 and Ki M8 in 3/4 cases.