Persuasion as a rhetorical action is the basic indicator of parliamentary speech. Therefore, it seems reasonable to ask whether the diarists describing the course of Sejm proceedings were aware of the use of persuasive acts of speech by MPs. The material analysed — 24 lexemes referring to the verbal acts of the speakers — was extracted from a dozen or so Sejm diaries documenting the proceedings in the Middle Polish period. The research has proven that diarists use verba dicendi, which indicate the result of a verbal act (e.g. namawiać, zagrzewać, pobudzać, obmawiać, napominać and animować) or that they pay attention to the persuasion process itself (e.g. dowodzić, emundować się, perswadować, wywodzić, konwinkować, allegować, okazować and remonstrować). In addition, the following nouns are used: dowód, wywód, komparacyja, argument, perswazyja, konkluzyja and racyja. Diarists deliberately use a variety of lexis because they strive to name the verbal acts of the speakers as precisely as possible.