The examinations were carried out in 33 patients (aged 21-69 years) with tuberculous and neoplastic effusions, before and during the treatment. 10 subjects with circulatory failure and pleural effusion a consisted control group. D-dimer level was detected using semiquantitative method (D-dimer Latex Test, Diagnostica Stago-Boehringer Mannheim), cells number and composition-using light microscope. All the groups demonstrated significant differences in the effusion D-dimer level before and during the treatment. Cells number was significantly higher in tuberculous and carcinomatous pleural effusion than in the control group. D-dimer level correlated with neutrophils percentage only in tuberculous effusions before the treatment. We found no correlation in D-dimer level and cells number and composition in neoplastic pleural effusion. We did not find any correlation in D-dimer level and cells number in blood.