This paper aims at contributing to the growing literature on the influence of public capital to the overall productivity levels. Using a panel of 20 Italian regions over the period 1970-1995 we estimate a production function which includes as inputs: units of labour, private capital and public capital. As a measure of public capital we compute the stock of public infrastructure at the regional level. A preliminary analysis shows that our series are cointegrated and this result ruled out the possibility of spurious regression in the estimation of the production function. Our results show that the estimated elasticity of output with respect to public capital is positive and statistically significant for the whole country and also for all the macro regions, with the exception of the Centre. Moreover, the disaggregation of public capital into functional categories emphasises the important role played by the infrastructures directly related to the economic production like transportation networks, telecommunications, airports.