This paper introduces a formalism (i.e. TDL), which allows LOTOS specifications to be given in the form of transition diagrams. We argue that being able to use transition diagrams, as a design notation for LOTOS, specifications would increase the quality of software produced via a formal method; and ultimately this enhances the LOTOS' acceptance by industry. The basis of our argument is that transition diagrams are well known and can be readily supported by tools. That is, transition diagrams (TDs) are a user-friendly and effective tool for the design of LOTOS specifications. In order to support the design process, we define a simple language (called TDL) for expressing and manipulating transition diagrams and for an intermediate language between transition diagrams and LOTOS specifications. We provide a group of rules for translating TDs in TDL to basic LOTOS. We also enrich the basic LOTOS with some meta-combinators to facilitate the translation from TDs to LOTOS.