Abstract: The subject of this study are the referential expressions that encode the O-participant in a transitive clause in the Modern Hebrew language. The goal of this study is to establish the significance of “definiteness” as a factor in asymmetric object marking for different types of referential expressions used by the Modern Hebrew speakers. For this purpose, the author considers the ways of expressing the category "definiteness" in various Modern Hebrew referential expressions that encode the O-participant in a transitive clause, and carries out a quantitative and comparative analysis of the ways of formalizing these expressions, using two research corpuses with a total volume of about 101 000 words. As a result of the analysis, it is concluded that, despite the clear correlation between the “definiteness” and the way noun phrases in the direct object role are constructed, “definiteness” is the only factor licensing asymmetric object marking for only one category out of the four considered, for proper names that are obligatorily marked. The remaining categories (definite noun phrases with other indicators of determination, indefinite noun phrases and pronouns) are all optionally marked within one or more types of referential expressions within each category. Of particular importance are the conclusions about the optional marking of referents encoded with the kol quantifier (55% of referential expressions with a quantifier and a relative pronoun are marked), partitive constructions (75% are marked), demonstrative and relative pronouns (48% and 66-85% are marked, respectively). It is proposed that for these types of referential expressions, there are additional factors that license asymmetric object marking in Modern Hebrew and that to determine them it would require further study of the discourse-pragmatic characteristics of referent-encoding expressions, including their referential status, status of animation, activity in discourse and degree of topicality.