Adhesion and biofilm formation by Pseudomonas putida was studied using suspended carriers in laboratory airlift reactors. Standard, roughened, hydrophobic, and positively charged glass beads, sand, and basalt grains were used as carriers. The results clearly show that in airlift reactors hydrodynamic conditions and particle collisions control biofilm formation. in the reactors, on surfaces subjected to different shear levels, biofilm formation differed considerably. This could be described by a simple growth and detachment model. Increased surface roughness promoted biofilm accumulation on suspended carriers. The physicochemical surface characteristics of the carrier surface proved to be less important due to the turbulent conditions in the airlift reactors. Adhesion of P, putida to glass beads was poor, and results of an adhesion test under quiescent conditions were not predictive for adhesion and subsequent biofilm formation under reactor conditions.