Abstract Gelatinases (MMP-2 and MMP-9) play a key role during invasion and metastazising of malignant cells and they have been shown to be associated to invasive phenotype and poor prognosis in several solid tumours. However little is known about their role in hematological malignancies. In the present work, gelatinase expression and its clinicopathological correlations were studied with immunohistochemical staining in 10 cases representing normal bone marrow aspirate smears, 123 cases representing diagnostic bone marrow samples of patients with different leukaemias (35 AML, 7 CLL, 6 CML, 75 ALL), 67 diagnostic paraffin-embedded lymph node biopsies from patients with Hodgkin's lymphoma and 57 biopsies from patients with non-Hodgkin's lymphomas. The lymphoma samples were also stained with factor VIII antibody to evaluate the extent of new vessel formation and the non-Hodgkin's lymphoma cases also with tissue inhibitor of metalloproteinases -1 (TIMP-1) antibody. CLL did not express either of the MMP enzymes, while CML in the chronic phase expressed strongly both of the enzymes. In ALL, gelatinase expression was weak and detectable in pediatric cases in only 12.7% and in the adults in 65% of the cases. In adult ALL, MMP-2 expression correlated strongly with an extramedullary and invasive pattern of disease presentation. In AML MMP-2 positivity had markedly favorable prognostic and predictive power. In lymphoma studies, no correlations could be detected between gelatinase expression and the clinical parameters of invasion. MMP-9 positivity was related to the presence of B symptoms, which difference was statistically significant in Hodgkin's lymphoma. In Hodgkin's lymphoma, strong MMP-9 expression also implicated decreased neovascularization. In both lymphoma types, strong MMP-9 expression correlated with unfavorable prognosis, which difference was statistically significant in non-Hodgkin's lymphomas and remained as a tendency in Hodgkin's lymphoma. MMP-2 had statistically significant association with a favorable prognosis in Hodgkin's lymphoma. Combination of the results of both stainings further increased prognostic power. All together these findings implicate that gelatinases could be used as prognostic tools in AML and lymphomas albeit this needs to be verified in larger materials.