Dissolved organic carbon from seawater and freshwater was separated into hydrophilic-base, hydrophilic-neutral, hydrophilic-acid as well as hydrophobic-base, hydrophobic-neutral, and hydrophobic-acid fractions which were used to form conditioning films on hydrophilic stainless steel and aluminium as well as on hydrophobic polypropylene and perspex. Water contact angles indicated that every conditioning film modified the wettability of clean substrata; the wettability of hydrophobic surfaces was generally increased and that of hydrophilic surfaces decreased. Adhesion results with carbon-and nitrogen-limited phenotypes of the Gram-negative bacterium SW8 suggested that adhesive or adhesive components of conditioning films were not associated with particular chemical fractions. The proportion of conditioning films derived from water fractions which modified the attachment of carbon-limited SW8 on hydrophobic and hydrophilic substrata was 29 and 71%, respectively. These films generally reduced the number of organisms on hydrophobic substrata but increased it on hydrophilic materials. No fraction produced films which either altered the adhesion of carbon-limited organisms on all substrata or which did not affect adhesion of the phenotype. The adhesion of these cells to stainless steel and perspex depended on the concentration of film-forming material in solution. Mixing of a fraction which produced adhesive films with material from another fraction whose films were less adhesive produced hybrid films which retained carbon-limited SW8 in amounts which were proportional to the relative content of organic matter from the adhesive fraction. Attachment of the carbon- and nitrogen-limited phenotypes differed on 69% of surfaces coated with films from natural water fractions. Carbon-limited cells attached in higher numbers than nitrogen-limited SW8 on 82% of these surfaces. Nitrogen-limited SW8 generally adhered less to conditioning films from seawater than carbon-limited cells. The contact angle values did not correlate with the numbers of SW8 attached to conditioned substrata.