A range of monthly series are currently available giving indications of short-term movements in output in the UK. The main aim of this paper is to suggest a formal and coherent procedure for grossing these monthly data up to represent the whole of GDP. Although the resultant estimates of GDP would be worse than those obtained by direct measurement, they should be more satisfactory than simply making an informal inference from whatever monthly data are available. Our examination of the efficacy of the method for estimation of the state of economic activity indicates a rather satisfactory outcome.