Total N-acetylneuraminic acid (NANA) and lipid-bound sialic acid (LSA) were evaluated as indicators of tumour burden in a range of human tumours and also an animal model system. For human bladder carcinoma, both serum and urinary total NANA were found to lack the sensitivity required for use as markers for small tumour burden. However, serum NANA levels were significantly elevated in cases of advanced disease, thereby implying a role for this marker as a supplementary parameter in the clinical mdnitoring of high stage bladder carcinoma. In the evaluation of total serum NANA as an indicator of human prostate tumour burden, NANA levels were monitored m 10 patients undergoing treatment for advanced disease over periods ranging from 3 - 6 months. Individual isolated NANA determinations did not always reflect tumour burden. This marker displayed characteristics of an acute-phase reactant, whereby a large incidence of false positive results indicated a deficiency in the specificity of NANA as an indicator of tumour burden. However, serial determination of NANA was found to be useful as a means of monitoring patient response to therapy. Using an animal model system, both total serum NANA and serum LSA were evaluated as tumour markers for Landschutz ascites tumour (LAT). Prolonged monitoring of serum NANA and LSA levels showed that LSA more accurately reflected the extent of tumour burden.