The report presents an investigation of the role of the sulfate balance in blended binders with slag (ground granulated blast furnace type, GGBS) or fly ash (low calcium type) in achieving improved sulfate resistance (SR) when using non-SR CEM I. The investigation involved experiments with sulfate-doped vs. undoped blended binders, pastes and mortars with and without exposure to sulfate attack, which was induced by immersion in Na2SO4 solution using a laboratory method. The results reveal the benefit of a sulfate level adjustment to promote improved behaviour during sulfate attack: doped blends yielded lower expansion during sulfate attack and reduced internal damage compared to undoped alternatives. Sulfate-doping increased the potential of slag and fly ash to mitigate sulfate attack with non-SR cement.