In July and August 1990, symptoms of verticilliosis were common in maturing crops of linseed sampled in Hertfordshire, UK and throughout Germany. Grey chlorotic or brown stripes were observed on green stems; on maturing, light brown stems the stripes were dark brown. Symptoms frequently extended along the whole length of the stems and branches up to the capsules, and often spread completely round the stems. Black microsclerotia developed abundantly in stems with these symptoms and Verticillium dahliae was consistently isolated from them. The incidence of verticilliosis increased from 50 to 100% in untreated plots (cv. Antares) between 8 and 22 August at Rothamsted, UK and was not decreased greatly by fungicide treatments. The incidence ranged from 49 to 98% on cultivars and breeding lines in trials at Thule, Germany on 9 September. V. dahliae was isolated from seed from Rothamsted plots at an incidence of < 10%