Marek's disease is an important lymphoproliferative neoplasm of chickens, caused by oncogenic strains of herpes virus. Visceral lymphomas and invasion of both central nervous tissues and peripheral nerves by lymphoid cells are common findings. Matrix metalloproteinases (MMPs) are a group of enzymes responsible for extracellular matrix degradation and tumour metastases. The localisations of MMPs in tumour cells were evaluated immunohistochemically. As a result, positive reactions for MMP-9 and MMP-2 enzymes were found in the lymphoid tumour cells. These enzymes may take part in the pathogenesis of Marek's disease causing extracellular matrix degradation and metastasis.