There is an urgent need to expand our knowledge of both the nature of the toxigenic fungi that are widespread on economically-important plants and the effect of their toxic secondary metabolites on human health. Informa­ tion about the production of mycotoxins by plant pathogens, particularly by species of Fusarium, Aspergillus and Penicillium, their occurrence in infected plants, as well as their role in the plant-pathogen interaction, for example as virulence/pathogenicity factors, is a pre-requisite for preventing plant disease and hence for reducing the Ievels of mycotoxin contamination. Fusarium infections in cereals and other crops are a particular problern world-wide and recent epidemics on wheat in Europe, the USA and Canada have again focused attention on this problem. Fur­ thermore, species ofAspergillus and Penicillium and their related mycotoxins, particularly Ochratoxin A, represent another consistent problern on cereals and grapes, especially in Europe where 40% of the global grape crop is grown. The aim of this publication is to gather together specialist updated reviews based on papers originally presented during a Workshop of EU Cost Action 835 entitled 'Agriculturally Important Taxigenie Fungi', held in Rome, 7-8 October 1999 at the Plant Pathology Research Institute. We hope the diversity of the contents will stimulate discussion, encourage the sharing of information and result in cross-fertilization of ideas needed for the solution of the present problems. This special issue will be of particular value to interdisciplinary scientists and especially mycologists, mycotoxicologists, plant pathologists and those concerned about the quality of food and food products.