Total sialic acid (TSA) and "lipid-bound" sialic acid (LSA) were evaluated in comparison to carcinoembryonic antigen (CEA) and ferritin and neuron specific enolase (NSE) in 152 untreated patients with primary lung cancer, 107 benign pulmonary disease patients and 207 notmal controls. The mean concentrations of TSA, LSA and CEA in lung cancer patients, were significantly higher than in benign and normal controls (p less than 0.001), while the mean ferritin and NSE levels were significantly higher than in normal controls only (p less than 0.001). At the designated cut-off serum levels, sensitivities of the five markers for lung cancer were in decreasing order: TSA 86.5% (greater than 80 mg/dL), LSA 77% (greater than 20 mg/dL), CEA 46.4% (greater than 5 ng/mL), ferritin 36% (greater than 300 ng/mL) and NSE 34.5% (greater than 12.5 ng/mL). Using the benign pulmonary values as negative controls the specificity of each marker was as follows: CEA 88%, ferritin 72%, NSE 58%, TSA 44% and LSA 44%. In small cell lung cancer (SCLC) patients, NSE mean concentrations and sensitivity were significantly higher than in non-small lung cancer (NSCLC) patients (9.63 +/- 4.4 versus 23.54 +/- 16.9, p less than 0.001 and 74% versus 21.4% respectively). While in NSCLC patients only CEA levels correlated well with the stage of the disease, in SCLC patients concentrations of TSA, LSA and ferritin were significantly higher in extensive than in limited disease stages. These preliminary data suggest that, although TSA and LSA are highly sensitive markers in lung cancer, their specificity is low.