To determine whether a -L-fucosidase (ALF) and sialic acid (SA) are sensitive markers in malignant pleural effusions, their levels were determined both in' serum and pleural fluid of 64 consecutive patients with pleurisy and in serum of 23 healthy individuals chosen as the control group. These two markers were elevated in malignant and nonmalignant groups as compared to controls. However, these increases were significant only for serum SA concentrations (p<0.05). No significant differences between malignant and nonmalignant groups regarding serum ALF (sALF), pleural ALF (pALF), serum SA (sSA), and pleural SA (pSA) levels were found. Neither ALF nor SA is a valuable tool in the detection of malignant pleural effusions.