Using scanning electron microscopy (SEM), differential interference contrast microscopy (DICM) and cytochemical staining techniques, preliminary observations have been made on the mechanisms of attachment of some common, marine, benthic fouling blue‐green algae ("cyanobacteria") isolated into culture from various toxic and non‐toxic surfaces in Langstone Harbour, south coast of England. Blue‐green algae investigated included species ofCalothrix, Dermocarpa, Plectonema, PhormidiumandXenococcus. The blue‐green algae are rapid colonisers and can make an important contribution to the pioneering communities on both toxic and non‐toxic surfaces. A characteristic feature of the colonization process is the production of variable quantities of extracellular polymeric substances (EPS) which appear to function as adhesives. Cytochemical staining revealed the EPS to be an acidic polysaccharide and, therefore, chemically similar to the EPS produced by sessile diatoms. It is suggested that the EPS additionally assists in cell motility, acts as an antidesiccant and may influence the fouling process by combining with antifouling paint toxins and modifying the surface energy of substrata.