A differential mass-balance model for the uptake of organic chemicals into plants from soil and air will be is presented and discussed. Processes considered are root uptake, gaseous and particle deposition, volatilization from leaves, degradation and growth. The model was incorporated into the European Union System for the Evaluation of Substances (EUSES) as part of the human indirect exposure calculation. The volatilization of organic chemicals from contaminated soil and the subsequent sorption into foliage is investigated with a diffusion/dispersion model for the two media-- soil and vegetation. The results are used to explain measured concentrations of PCDD/F, PCBs, PAHs and pesticides from laboratory studies, controlled outdoor studies and field observations in various crops and pasture.