In a steady state biofilm culture, dissolved organic carbon (DOC) distribution between catabolism and anabolism can be described by a ratio of the DOC channeled into carbon dioxide (S-CO2) to the DOC converted into biomass (S-g). Based on a balanced oxidative reaction of DOC, a S-CO2/Sg-dependent observed growth yield (Y-obs) model was developed for biofilm culture and was verified with literature data. Growth and detachment forces are two decisive factors in biofilm process. The detachment force (D-f) normalized with respect to the growth force (G(f)) was introduced to describe the interaction between the biofilm growth and detachment processes. Biofilm metabolism and structure were closely related to the D-f/G(f)-ratio, and biofilm community could metabolically respond to changes in growth and detachment forces. A proper balance between growth and detachment forces is crucial for development of a compact and stable biofilm. The proposed D-f/G(f) concept provides a theoretical basis for experimental data obtained at different growth and detachment forces to be interpreted in a unified sense. Biofilm structure may be manipulated by controlling the D-f/G(f) ratio. (C) 2002 Elsevier Ltd. All rights reserved.