This article analyses Imperial Germany's legendary coalition of landed aristocracy and heavy industry around a policy of tariff protection. Using a simple model of voting behaviour, where party affiliation serves as a partial intervening variable between constituency interests and legislative votes on trade policy, I test hypotheses derived from three different interpretations of the ‘marriage of iron and rye’. Roll-call votes from four key divisions in the Reichstag are analysed in a number of forms, ranging from cross-tabulations to conditional logistic regression. Ronald Rogowski's ‘factor endowment’ model offers an important dynamic perspective that is lacking in the others, but his model must be reconciled with anomalies that arise in the short run. Rather than attempting to disentangle political party ideology from constituents' interests, more insight may be gained from understanding why the effects of the two causal factors were not fixed, and how they varied over time.