Aim of this study was to estimate the diagnostic possibilities of computed tomography (CT) and magnetic resonance imaging (MRI) in the assessment of treatment effect in malignant lymphomas. In the period of 1998 to 2002, 196 patients with histologically proven malignant lymphoma were examined in the Department of Tomography of Kaunas University of Medicine Hospital. The data were processed with SPSS 10.1, including application of standardized t-test and classification of Fisher's statistics. In this group the density of lymphomatous masses prior and post treatment has no difference on CT images, thus the differentiation of active tissue and relapse is not possible. On MR images the difference of signal intensity of the active component (not treated) and fibrous remnant is significant. MRI is a radiological method which provides information about activity of lymphomatous tissue and is able to delineate the active component (recidive or partial remission) and inactive remnant (total remission) of the tumor mass and thus facilitating the diagnosis of possible relapse of malignant lymphomas for hematology, chemotherapy and radiotherapy specialists.