The development of the root system of cowpea cv. 'Prima' seedlings was studied during the period 3 to 12 days after germination. Seedlings were grown on filter paper between vertical glass sheets within a root chamber. The emergence and initial elongation of secondary, and then tertiary, roots coincided with a depression in elongation rate of the primary and then secondary roots respectively. Four classes of secondary lateral roots, each with distinct, quantitative differences in growth potential, were clearly identified. Secondary roots with high growth potentials alternated with others with much lower growth potentials along the entire length of the primary root those with the highest potential being located midway along the primary axis. An average of 35 secondary root were developed, of which 13 produced tertiary roots. The mean total length of the cowpea seedling root system 12 days after germination was about 6 m. The growth pattern of secondary root appear to be determined within seven to ten days after the onset of germination. Soil conditions during seedling establishment may, therefore, determine the theoretical potential and linear limits of soil exploitation if root growth potential and growth pattern are both affected. There may be consequences of inherent differences in root growth potential on infection and nodulation of the cowpea root system by Rhizobium.