Abstract An intercrop of one row of sorghum ( Sorghum bicolor (L.) Moench) and three rows of groundnut ( Arachis hypogaea (L.)) and sole crops of the two species were grown with limited water supply on an alfisol in central India. The faster growth rate of intercropped sorghum was the result of a greater fraction of light being intercepted rather than a higher efficiency ( e) of conversion of light into dry matter. In intercropped groundnut, there was a strong correlation between the growth rate of each row and the fraction of light it intercepted, and although shading by the sorghum reduced the latter in comparison with the sole crop, e was higher. Two patterns of response were evident in the intercropped groundnut. Those involving resource use (light and water) and dry matter production were lowest in the outer two rows and highest in the centre row, while those involving development (e.g. pod numbers) increased from the least shaded row to the most shaded. Competition for water by the more aggressive sorghum was thought to be responsible for the first response, and temperature and water potential gradients caused by differing degrees of shading for the second. The effect of the interaction of these two responses on the harvest index is discussed.