The article is an overview of some elements of humanist 'topoi', or commonplaces, which are included in letters by Mutianus Rufus. These elements have been confronted with an analogous topic in the writings of Erasmus Roterodamus. Mutianus' esoterism, or Pythagoreanism, as he used to call it, forms a framework for them. There is an important element, which stands in the strict opposition to the values and practice of humanists in general, as well as Erasmus in particular, i.e. Mutianus did not publish his letters, and their recipients were not allowed to do it. Other elements, although partially come together with Erasmus' humanist 'topoi', often have completely different meaning. Comparative analysis unveils the differences between Mutianus' and Erasmus' comprehension of identical as well as very similar religious problems, e.g. the Christian rituality, and the problems remaining within intellectual and spiritual culture, such as the way of understanding the essence and value of philosophy, the problem of the presence of human spirit in literary works, and questions pertaining to literary culture and literary techniques, such as ornamenting their own Latin texts with Greek and national proverbs.