Laboratory and greenhouse experiments were conducted to formulate predictive models for the uptake of cadmium by Jelly bean (Phaseolus vulgaris L.), grown in sludge-treated soils, on the basis of soil and plant-root properties. The values of the porous system self-diffusion co-efficient (Dp) of cadmium fulvic acid complexes in soils were higher than those when Cd was applied as inorganic salts. Pot experiments were conducted with ten sewage sludge-treated old alluvium, non-calcareous, non-saline (Vertisol) soils of Patna wherein a Jelly bean crop was grown after soil treatment with 0 and 5 mgkg(-1) isotopically tagged and organically complexed Cd. The results indicated that the application of Cd through Cd-FA in soils did nor influence the dry matter yield and root radius (r(0)), root density (L-V) and half distance between the roots (r(h)) of the crop, though if significantly increased the concentration of Cd in the plants and its uptake by the crop. The soil organic carbon content, cation exchange capacity, clay content pH and EC were used to predict uptake of Cd by the crop. The root parameters and porous system self-diffusion co-efficient of Cd-FA in soils were able to predict the Cd uptake by the crop with very high levels of confidence. The modified form of the mathematical model of Baldwin et al. (1973) (Plant Soil, 38, 1973, 621-35) was found to be useful in predicting the rate of uptake of Cd by Jelly bean grown in sludge-treated soils.