This paper studies the role of two different types of motivation that have been proposed to explain the use of subject personal pronouns in Spanish, namely their function as indications for the addressee to identify the subject's referent, and their suitability for expressing informational values such as contrastiveness or focus. This study focuses exclusively on third-person forms and relies on conversational data. The distribution of third-person pronouns is analysed combining qualitative and quantitative approaches. It will be argued that the informational and referential properties of subject personal pronouns are by themselves insufficient to account for their expression, their occurrence depending crucially on their activation through the previous use of units of the same type.