Acidic glycoconjugates represent the major non-fibrous macromolecular components that form the extracellular and cell-associated matrices of all animal tissues. The constituent molecules are principally structural glycoproteins and proteoglycans. While their protein component is determined by gene pools, it is the polyanionic (acidic) nature of the polysaccharides, determined by their degrees of carboxylation and sulphation, which confers both functional and diagnostic status on these molecules. Sulphated glycoconjugates in the basal laminae have been reported to play a role in tumour invasion and metastasis. In this study, we used cationic colloidal gold together with transmission electron microscopic methods to compare the expression of acidic glyconconjugates in the basal lamina of both normal rat tongue mucosa and experimentally induced oral carcinomas. Results indicated that heparan sulphate rich glycoconjugates were predominant and were mostly confined to the lamina lucida of the basal lamina in normal oral mucosa. Conversely, observation of basal laminae associated with induced carcinomas showed less intense and more widely dispersed gold labelling for heparan sulphate. The observed differences in gold labelling may reflect modified metabolism of sulphated glycoconjugates or result from the action of degradative enzymes in the induced tumours.