The thesis deals with manifestations of lexical dynamics in the language of Internet discussion forums. The chosen communication sphere is typical for its creativity and spontaneity, respectively active exchange of lexical means and the effort for fresh expressions. For these reasons, the language of discussion forums on the Internet is a suitable material basis for the confrontational description of lexical innovations in contemporary Bulgarian and contemporary Czech. The theoretical part of the thesis defines the notion of neologism and the terms connected with it, as well as the specific features of Internet communication. In the practical part, a structural and semantic analysis of Czech and Bulgarian neologisms is carried out, and considering that a large part of the new lexicon used in the discussion forums is borrowed mainly from English, more attention is paid to the interpretation of the meaning of these loanwords and the ways of their adaptation in Czech and in Bulgarian.