The influence of different forms of substrate administration (either through the vapour phase or the liquid phase) on growth of two bacterial strains on biphenyl, 2-chlorobiphenyl, and 3,5-dichlorobiphenyl has been investigated. During growth with all three compounds, the availability of the substrate for the cells turned out to be the growth-limiting factor, even in liquid culture with excess substrate supplied to the medium. Growth on biphenyl and 2-chlorobiphenyl could be greatly enhanced if the substrate was distributed on a folded filter providing a large surface, which was placed in the vapour phase of the culture flask. This was not possible in the case of 3,5-dichlorobiphenyl. Here growth accelerated after accumulation of a yellow meta cleavage product. Through measurement of the surface tension it was shown that this yellow compound possessed detergent-like activities, increasing the amount of 3,5-dichlorobiphenyl dissolved in the medium.