We investigate the effect of specialisation upon the level of metropolitan wage per worker. Specialisation is measured by the share of metropolitan earnings in each of five traded goods and services sectors. Sectoral specialisations are assumed to be determinants of location-specific productivity, which in turn is treated as a term in a metropolitan production function. Panel data are used for estimating that production function for 313 metropolitan areas in the US, over the long period 1969-96 and two shorter periods. We find that some specialisations raise average metropolitan wages, some lower it and some have no effect, and that the effects of specialisation differ by time-period.