Knowledge intensive services (KIS) have a key role in the creation and commercialisation of new products, processes and services. They are fundamental as holders and creators of innovation, both technological and organisational.
Nevertheless, little is known about the factors that explain why some firms use more than other these services (technological advice, applied research, strategic consultancy, engineering, etc.). In this paper, using a database of more than 2.000 firms, the factors that explain the use of KIS by small and medium firms are analysed. The most consistent conclusions of the available studies show that the demand of services increases with the size of the user firms. Also, other variables as the age, sector, localisation, innovation level and exports are examined.