Opinion leadership is a concept that became a subject of several research studies in the second half of the twentieth century. With their work on personal influence, Katz and Lazarsfeld have shred the idea of the power of mass media. They showed, that information reaches the broader audience with the intervention of opinion leaders. In this dissertation we have applied the theory of opinion leadership, which was valid for traditional markets, to the use of online communication. Our aim was to find out, which are the similarities and differences in the attributes of trustworthy 'old' and online opinion leaders and what differences have online opinion leaders established when communicating with consumers. Since the opinion leadership process is presented with the model of two-step flow of communication in the classic studies, we included a detailed discussion of this model and adjusted it to the online environment, in which communication is no longer linear and two-step, but multidimensional and multistep. Knowledge, good communication skills, integrity and character, self-confidence, personal strength and innovativeness are the unchanged characteristics of trustworthy opinion leaders. Good knowing and common use of computer and internet, proneness to risk-taking, entrepreneurial orientation, obsession with creating new wealth, lower levels of conservatism, great passion, imagination and extraversion are the specific characteristics of online opinion leaders. The last characteristic has not been fully explained and is in this dissertation suggested for further research.