A complex seven species model community, including bacteria and fungi, was selected from organisms isolated from the walls of an industrial flowing water system. Growth rates of the species were determined in single and mixed batch culture growth. The rates were found to be significantly higher in mixed culture for Pseudomonas alcaligenes andFlavobacterium indologenes and higher in single culture forXanthomonas maltophilia, Rhodotorula glutinis and Fusarium solani, whereas no significant difference was recorded forAlcaligenes denitrificans and Fusarium oxysporum. All species attached to PVC in single and mixed culture to form biofilms.Xanthomonas maltophilia, Alc. denitrificans, Ps. alcaligenes andF. solani biofilm cell densities cm-2 were significantly higher than attachment of the component species in mixed culture. Statistical analyses showed a significant difference in rate of colonization between single and mixed cultures for some species. No significant difference was noted between mixed culture cell densities cm-2 at laminar flows of Reynolds number 2·7 and 5·4.