The quality of products produced by dairy manufacturing plant is threatened when bacteria attached to and growing (biofilm formation) on stainless steel are released into the product stream. The adhesion of bacteria to the surface is the first stage in this process and enables subsequent proliferation and release. In the present trial, thermo-resistant streptococci were found to adhere preferentially to stainless steel and zinc substrates compared with other metal and glass substrates and more bacteria adhered to 316L than to 304L, grade stainless steel. The adhesion of thermo-resistant streptococci to samples of 304 stainless steel with a range of surface roughness values (R-a 0.5-3.3 mu m) or with typical flaws was found to be largely independent of the substrate topography although bacterial entrapment may occur at 0.9 mu m.. The rate of adhesion of thermo-resistant streptococci was enhanced in the presence of a hydrophilic substrate, negative electrostatic forces and/or the presence of an oxide coat. (C) 2000 Elsevier Science Ltd. All fights reserved.