This paper examines the hypothesis that corporatist intermediation by party governments facilitates incomes policy formation and is effective in reaching agreements between employers and trade unions as well. A social democratic party in government would positively enhance this process. Investigating this for the Netherlands between 1965–2000, two puzzles emerge. The first puzzle is that coalition governments of Social and Christian Democracy fall short of expectations despite their commitment to corporatism. The second puzzle is that the relationship between Social Democracy and effective corporatist intermediation is positive but cannot sufficiently account for the variation in agreements on Dutch incomes policy. That variation can be better understood as induced by institutional change, economic development and external vulnerabilities. The Dutch case study shows that the performance of a social democratic party in government in a corporatist context is less directly effective than the literature often has suggested.