The aim of this paper is to describe and analyse the long-term process of paradigm levelling within the IV-verb-class of Czech verbs. This process has been in progress since as early as the 17th century. While in its first stage, the ending '-ejí' spread to the verbs of the 'prosí' and 'trpí' conjugation types, at the end of the 19th century the development began to move in the opposite direction. In 1993, the process finally resulted in the 'oni sází' form being codified alongside the 'oni sázejí' form. However, three inquiries into this variation in the sphere of public communication show that the '-í' form occurs in spoken texts rather than in written ones and that its incidence varies from verb to verb. The more frequent incidence of the '-í' form was only detected in a small group of verbs.