This paper employs the hedonic regression technique to construct constant‐quality price indices and quality change indices for two agricultural inputs ‐ tractors and fertilisers ‐ over the period since World War II in the UK. The technique is described and related to productivity measurement in order to show its relevance for measuring price changes for inputs subject to technological improvement. Problems of application are discussed with reference to the two inputs. The constant‐quality price indices derived for tractors and fertilisers are briefly compared with available ‘official’