Canada Western Red Spring (CWRS) wheat (Triticum aestivum L. cv. AC Barrie) was grownl at twelve locations, over two growing seasons across western Canada, to study the impact of S fertilization on grain yield and quality of wheat. Treatments consisted of two rates of fertilizer S (0 and 20 kg ha-l) as ammonium sulphate and two rates of fertilizer N (26 and 100 kg ha-l) as urea in a factorial design. Soil and plant tissue tests were also evaluated for their ability to predict grain S concentration, grain N:S ratio, total S accumulation in the plant, and grain quality responses to S fertilization. Analysis of grain for total S, N, and N:S ratio accurately predicted the concentration of S, N, and N:S ratio in flour. Grain S concentration and N:S ratio were weakly correlated with both absolute and relative grain yield. Grain S concentration was strongly and positively correlated with loaf height, loaf volume, and oven spring; grain N:S ratio was negatively, but more weakly, correlated with these baking parameters. The improvements in baking quality were accompanied by an increase in dough extensibility and reduction in dough strength. Grain S concentration was positively correlated with dough extensibility and negatively correlated with maximum dough resistance, mixograph peak time, and work input to peak. Grain N:S ratio was negatively correlated with dough extensibility and positively correlated with maximum dough resistance and work input to peak. The improvements in baking and dough quality were associated with changes in the protein composition of flour. Grain S concentration was positively correlated with the proportion of soluble glutenin and negatively correlated with the ratio of insoluble to soluble glutenin in flour. Grain N:S ratio was negatively correlated with the proportion of soluble glutenin and positively correlated with the ratio of insoluble to soluble glutenin in flour. Sulphur fertilization increased grain yield at two of seven sites used for breadmaking quality evaluation. Application of S fertilizer also frequently improved the breadmaking quality, dough quality, and flour protein composition of wheat at four of these seven sites. All four sites where grain quality improvements were observed contained < 40 kg SO4-S ha-l prior to fertilization, a concentration of soil S regarded as marginally sufficient for grain yield. Also, at these four marginal S sites, the S concentration and N:S ratio of plant tissue samples collected at 50 % heading was < 0.15 % S and > l7:1, respectively. Sulphur fertilization increased the concentration of S in grain and reduced the N:S ratio in grain at all marginal S sites. The improvements in grain S nutrition were accompanied by significant improvements in loaf volume at two of the four marginal S sites when S fertilizer was applied in combination with 26 or 100 kg N ha-l, and at one more site where 100 kg N ha-l was applied. Sulphur fertilization increased loaf height and oven spring at three of the four sites. Application of S fertilizer also significantly increased dough extensibility at all four marginal S sites and reduced maximum dough resistance and mixograph peak time at three of four sites. Mixograph peak time was significantly reduced at the other marginal S site only in the presence of 100 kg N ha-1. Furthermore, S fertilization reduced the viscoelastic ratio and mixograph work input to peak at all four marginal S sites. Sulphur fertilization increased the proportion of soluble glutenin in flour and reduced the ratio of insoluble to soluble glutenin in the flour at three of four marginal S sites. Sulphur fertilization in the presence of 100 kg N ha-1 only, increased the proportion of soluble glutenin in flour and reduced the ratio of insoluble to soluble glutenin in the flour at the other marginal S site. At the three sites where soil SO4-S concentrations were > 40 kg ha-l, no yield and few breadmaking quality improvements were observed in response to S fertilization. For these high S sites, S fertilization did not increase the S concentration in grain at any site and reduced the N:S ratio in grain at only one site. At all four sites where grain contained <- 0.17 % S and an N:S ratio > 17:1, quality improvements due to S fertilization were consistently observed. At all three sites where grain contained S concentrations >-0.17 % S and N:S ratios < 17:1, breadmaking quality responses to S fertllization were infrequent...