THE ergot fungus, Claviceps purpurea (Fr.) Tul., is common on cereals and grasses throughout the temperate regions of North America1,2. It is often severe on rye (Secale cereale L.) and durum wheat (Triticum durum Desf.) and in recent years it has also been troublesome on Triticale (Triticum sp. × S. cereale) and on male sterile cultivars and lines used in the development of hybrid spring wheat (Triticum aestivum L.) at the University of Manitoba. Field observations in the past have indicated that some cultivars of either spring or durum wheat are more susceptible than others3, but experimental evidence of resistance has not been reported. We therefore investigated the variability of the infection reaction to C. purpurea in the cultivated cereals, aiming to find possible sources of resistance for use in the Triticale and hybrid wheat breeding programmes.