A multi-product, multi-input translog cost function is used to investigate the structure of Northern Ireland agriculture. The two-output four-input cost model utilizes duality theory to facilitate econometric measurement of partial elasticities of substitution between inputs for each year, the annual own- and cross-price elasticities of input demand, the annual overall scale economy parameter, and the annual rate of Hicks-neutral technical change. It also permits an assessment of cost complementarity between the two outputs. The results obtained are compared with a similar, earlier study (Ray, 1982) on United States agriculture, and with descriptive analyses of Northern Ireland agriculture.