AbstractBacteria of the genusPseudomonaswere screened for antagonistic activity towardsCeratocystis ulmi in vitro. Selected bacteria were then tested for their ability to suppress symptoms of Dutch elm disease in English elm (Ulmus procera) and Commelin elm (U. Xhollandica“Commelin”)in vivo. In a series of preventative bacterial injection experiments on English elm, no reduction in disease levels was obtained by comparison with non‐injected controls. In curative injections of Commelin elm, only a slight reduction of disease recurrence in treated trees was indicated. Bacteria showed limited upward distribution in the trees, but may have become well distributed within the roots. The significance of the results for the control of Dutch elm disease is disc