The aim of the study was the evaluation of angiogenesis processes in fibrosarcoma induced by 3-methylcholanthrene (3-Mc) in reference to the number of mast cells (MCs). 76 male Wistar rats were divided into 4 groups: two experimental (E) groups--after injection of 0.2 mg 3-Mc dissolved in olive oil (0.25ml), and 2 control (C) groups. In E1 group, 52 rats were killed after development of the fibrosarcoma; E(2)--10 rats were killed before development of the tumor; C(1)-8 rats received 0.25ml olive oil; C(2)--8 rats received no treatment. Tissue material was fixed in buffered formalin or Carnoy's and Bouin's fluid. Paraffin sections were stained with H+E and Azan methods, and with alcian blue-saphranine and toluidine blue. Immunohistochemical reactions detecting tryptase in MCs were also performed. Angiogenic objects (microvessels and single endothelial cells) were recognized using antibodies against factor VIII (vWF), P selectin (CD-62P), and CD-90. We found a distinct relationship between intensification of neoangiogenesis at the tumor periphery and increased number of MCs.