This article analyses the importance to a restorer of being able to determine beforehand what points may be of most interest for the extraction of polychrome microsamples in the specific case of carved altarpieces. The work on the main altarpieces of Siguenza Cathedral [Guadalajara), the Church of San Francisco in Tarazona [Zaragoza) and the Santa Maria in Calatayud [Zaragoza), promoted in all cases by the IPCE [Institute for the Spanish Cultural Heritage], has laid the necessary methodological groundwork for the planning and design of a specific protocol. This requires concrete knowledge of other parameters -documentary bases, scientific techniques, pictorial procedure, etc.- to establish the most suitable selection criteria in each case.