Rules for segmental duration has been studied in the context of a speech database that is under development in our department. The database search procedures include the same kind of context sensitive rules that are used in our speech synthesis project. This gives us the possibility to make a direct comparison to the database durations when developing durational rules for a text-to-speech system. Different kinds of speech material have been studied, including a novel and read sentences. Some different descriptive frameworks have been tried. A modified version of a rule structure suggested by Klatt has proven to be especially useful.