SummaryA range of fungi was screened for the ability to suppress symptoms of Dutch elm disease in European and hybrid elms under UK and Italian field conditions. The efficacy of the preventative inoculations varied Considerably between elm clones of differing resistance to the causal fungusOphiostoma novoulmi. On susceptible English elm,Ulmus procera, preventative inoculations with conidia ofVerticillium dahlias, Opbiostoma ulmiorOphiostoma piceae(OPH form) caused no reduction in final disease levels. OnU. x bollandicacv.‘Commelin’, pretreatment withV. dabliaeorO. ulmireduces final disease levels, but not significantly, On the elm clone Ca06 ofU. carpinifolia, and on the hybrid clones FL025 and 196–6, significant (p0.05) symptom suppression occurred in trees pretreated withO. ulmiorV. dahliae. On the more resistant elm clones 3–14 and Lobel, onlyV. dahliaewas an effective pretreatment (p0.05). Certain pretreatment fungi alone caused symptoms in some of the elm clones. Major difficulties in using this approach to control Dutch elm disease are discussed.The technical assistance by F. C. Baldwin, R. Brooker, S. A. Kirkand J. Roseat the Forest Research Station, Alice Holt, and by A. Fagnaniand F. Ferriniat CNR, Florence, as well as statistical advice from A. J. Peaceat Alice Holt, is gratefully acknowledged.The authors would like to thank the Pilkington Charitable Trust for funding the research in the UK and lsotron plc, Swindon, Berkshire, for gamma irradiating the conidial suspensions. The Italian contribution was supported by the National Research Council of Italy, special project RAISA, subproject no. 2, paper no. 2133. The authors also thank John GIBBS for helpful comments on the man