An experiment was conducted to study the root behavior and nitrogen (N) balance in pigeonpea-based Intercropping systems during the 1993 rainy season. Five crops (pigeonpea: ICP 1-6, sorghum: CSH 5, pearl millet: ICMV 221, groundnut: ICGS 11 and cowpea: EC 82-7) were used. All the plots received uniform basal application of 25 kg N ha^-1 as urea and 20 kg P₂O₅ ha^-1 as single superphosphate. The fractional contribution of N derived from air (%N_dfa) in legumes and from fertilizer (%N_dff) was determined by the natural ¹⁵N abundance and ¹⁵N tracer methods, respectively. A minirhizotron was used for the measurement of root length density (RLD) nondestructively. The RLD was significantly higher in cereals and pigeonpea/cereal than in legumes and pigeonpea/legume intercroppings. There was no significant difference in total N content among sole and intercropped pigeonpeas. The %N_dfa was significantly higher in pigeonpea intercropped with cereals than with legumes, suggesting that cereals are able to deplete soil N massively due to their high RLD and enhance the dependency of pigeonpea on biological N fixation. It is speculated that the enhancement of %N_dfa of intercropped pigeonpea depends on the extent of competition for the uptake of soil N in the deep Alfisol soil by roots of companion crops at the vegetative growth stage.