The effects of a combined fungicide and growth regulator treatment on the composition and dry matter digestibility of straw samples of winter wheat cultivars, Beaver, Brigadier, Hussar, Mercia, Riband, Genesis, Hunter, Spark, Cadenza and Flame, were compared. The samples were analysed for nitrogen, ash, fibre fractions and minerals. Nitrogen content of treated samples was reduced compared to the untreated control samples and in contrast the proportion of ash increased for all the treated samples. All samples were analysed by derivative thermogravimetry (DTG) to determine changes in fibre composition. Only six cultivars were analysed by chemical fractionation methods to determine changes in lignin, cellulose and hemicellulose content. The results from the two methods of fibre analysis were broadly similar. K, Ca, Mg and Na concentrations of the treated straw samples were found to be different to the untreated samples. Increase in dry matter digestibility (DMD) of treated straw was observed for all cultivars; the effects on Beaver, Brigadier, Mercia, Riband, Genesis, Hunter and Cadenza were most pronounced, but were less for Hussar, Spark and Flame. The potential impact of these changes in straw quality on organic mushroom compost preparation is briefly discussed. . P-Coumaric and ferulic acid components of cell walls of rye grass and their relationships with lignin and digestibility. Journal of the Science of Food and Agriculture 23:1347-1354. Hartley R D, Harris P J, Russell G E. 1978. Degradability and phenolic components of cell walls of wheat in relation to susceptibility to Puccinia striiformis. Annals of Applied Biology 88:153-158. Janzen R H, Kucey R M N. 1988. C, N and S mineralization of crop residues as influenced by crop species and nutrient regime. Plant and Soil 106:35-41. Jones D I H, Hayward M V. 1973. A cellulase digestion technique for predicting the dry matter digestibility of grasses. I. 1983. Enzymatic saccharification of wheat straw-differences in the degradability of straw derived from different cultivars of winter wheat. Journal of the Science of Food and Agriculture 34:433-439. Palmer F G. 1976. The feeding value of straw to ruminants. ADAS Quarterly Review 21:220-234. Priestley R H. 1981. Fungicide treatment increases yield of cereal cultivars by reducing disease and delaying senescence. European Mediterranean Plant Protection Bulletin 11:357-363. Reinertsen S A, Elliott L F, Cochran V L, Campbell G S. 1984. Role of available carbon and nitrogen in determining the rate of wheat straw decomposition. Soil Biology and Biochemistry 16:459-464. Savoie J M, Chalaux N, Olivier J M. 1992. Variability in straw quality and mushroom production: Importance of fungicide schedules on chemical composition and potential degradability of wheat straw. Bioresource Technology 41:161-166. Savoie J M, Minivelle N, Chalaux N. 1994. Estimation of wheat straw quality for edible mushroom production and effects of a growth regulator. Bioresource Technology 48:149-153.