The study of the partitioning of PCBs and similar hydrophobic organic chemicals between solid and aqueous phases, such as suspended particles and the water column, has normally been approached from an equilibrium thermodynamic point of view. The kinetics of the uptake process have received some study but this has been limited. This paper presents a rationale for the importance of HOC uptake kinetics. A simple kinetic model is developed and applied to PCB in suspended particles and surface waters. It describes, in practical terms, many of the reported behavioral characteristics of Kd, the partition coefficient, observed both in the laboratory and in the field.