This article analyses the cases of enantiosemy (semantic polarity) of Russian dialect and literary words with the prefix bez-, as well as examples of synonymy among bez-prefixed lexemes and their prefixless motivating lexemes. The latter phenomenon is usually due to the process of desemantisation of the prefix bez- and acquisition of amplification functions. Among the main reasons why the prefix bez- loses its basic meaning (the meaning of absence or shortage) are: deetymologisation of a lexeme; general expressivity of a word to which the prefix bez- is attached; negative-expressive «inertia» of semantic field; the tendency of semantic negation to be expressed through a formal indicator. Emergence of enantiosemy, on the one hand, can be explained by the phenomenon of homonymy, and, on the other hand, can be independent of it. The development of opposite meanings not associated with homonymy is usually due to different interpretations of «ambiguous» inner form of words: exchange of subject-object relations, shifts of «drifting» evaluative semantics contained in lexemes towards one or another extreme (this is particularly common with emotive words and temporal or quantitative measure designations), etc. Also frequent are cases of enantiosemy (including dialect enantiosemy) as a result of desemantisation of the prefix bez-.