This paper deals with theoretical problems found in the work that is being carried out for annotating semantic roles in the Basque Dependency Treebank (BDT). We will present the resources used and the way the annotation is being done. Following the model proposed in the PropBank project, we will show the problems found in the annotation process and decisions we have taken. The representation of the semantic tag has been established and detailed guidelines for the annotation process have been defined, although it is a task that needs continuous updating. Besides, we have adapted AbarHitz, a tool used in the construction of the BDT, to this task. Key Words: Theoretical Problems in Semantic Annotation, Representation of Semantic Roles, Lexical Resources