Members of a triple-species 3-(3,4-dichlorophenyl)-1-methoxy-1-methyl urea (linuron)-mineralizing consortium, i.e. the linuron- and 3,4-dichloroaniline-degrading Variovorax sp. WDL1, the 3,4-dichloroaniline-degrading Comamonas testosteroni WDL7 and the N,O-dimethylhydroxylamine-degrading Hyphomicrobium sulfonivorans WDL6, were cultivated as mono- or multi-species biofilms in flow cells irrigated with selective or nonselective media, and examined with confocal laser scanning microscopy. In contrast to mono-species biofilms of Variovorax sp. WDL1, the triple-species consortium biofilm degraded linuron completely through apparent synergistic interactions. The triple-species linuron-fed consortium biofilm displayed a heterogeneous structure with an irregular surface topography that most resembled the topography of linuron-fed mono-species WDL1 biofilms, indicating that WDL1 had a dominating influence on the triple-species biofilm architecture. This architecture was dependent on the carbon source supplied, as the biofilm architecture of WDL1 growing on alternative carbon sources was different from that observed under linuron-fed conditions. Linuron-fed triple-species consortium biofilms consisted of mounds composed of closely associated WDL1, WDL7 and WDL6 cells, while this association was lost when the consortium was grown on a nonselective carbon source. In addition, under linuron-fed conditions, microcolonies displaying associated growth developed rapidly after inoculation. These observations indicate that the spatial organization in the linuron-fed consortium biofilm reflected the metabolic interactions within the consortium.