Recent empirical studies have found significant evidence of departures from competition in the input side of the bread, breakfast cereal and margarine endproduct markets. In this study we specify a general duality model of profit maximisation that allows for imperfect competition in the input and output markets of the grains and oilseeds industries. The model allows for a variable proportions technology and does not impose restrictions on the relationship between conjectural elasticities in each market. Aggregate Australian data is used to implement the model and draw inferences concerning the presence of market power.