The av. reactant diffusivity and blofilm av. d. data detd. In a series of blofilms varying In thickness enable their distribution patterns to be established as functions of a current coordinate in the biofilm. The resulting equations take on the form related to the geometry of the Mm-growing substrate and to the functions adopted to describe the av. d. and diffusivity In relation to film thickness. Lin. regression suffices to det. the correlation parameters. The diffusivity and esp. the av. d. varied considerably In the blofilms grown on small spherical particles used In 3-phase fluidization bioreactors. The data reported on Pseudomonas putida microorganisms applied in a 2- and a 3-phase fluidization bioreactor were used to show how the biofilm efficiency and thus the overall process rate was affected.