The effect of auxin of shoot origin on the growth and development of the root system of Pisum sativum L. cv. Kelvedon Wonder was investigated. Root growth was reduced when auxin transport from shoot to root was interrupted, but this could have been caused by a reduction in assimilate supply rather than a deficiency of auxin. Shoot removal, however, markedly reduced the number and total length of secondary roots produced and a 1% IAA–lanolin paste applied to the cut stump compensated to a large extent for shoot removal, markedly increasing secondary root growth in de-shooted plants. It is suggested that auxin produced by the shoot may influence the growth and development of the root system.