Microeconomic capital goods theory was utilised to provide a theoretical framework on which a dynamic econometric model was based. Econometric procedures were then employed in an analysis of sheep producers' decision making regarding the annual supplies of wool, lamb and mutton, and annual changes in the inventory levels of sheep, lambs and ewes maintained for breeding purposes. Estimates show that wool prices provide the long-run stimulus for increases and decreases in the sheep flock while mutton and lamb prices are responsible for short-run changes in flock composition. Substitution between sheep and beef cattle is of considerable importance although no significant substitution between sheep and cropping could be found. Seasonal conditions proved to be an important short-run supply shifter, affecting both numbers and composition of the sheep flock.