The paper attempts to analyse some aspects of the economic evolution of a medium-sized Spanish town during a decisive phase of the contemporary urban growth of the country, the inter-war period, through the analysis of the local entrepreneurial structure. The aim was to examine the gradual transformation of this town into a commercial and service economy. The tertiary sector, strongly linked to port functions (goods traffic, fishing and by-products, migration flows, etc.), retail and wholesale, was a significant factor (together with other traditional urban functions, such as military, administration, etc.), in the diversification of the urban economic structure. Besides, an effort was made to determine if the local economy followed the socio-economic and political junctures of this period, comparing that behaviour with the pattern of other Spanish towns.