Background. In linguistics, it is customary to study individual language phenomena at one level of the language system. Despite this rather artificial demarcation, it is obvious that units of all structural levels actively interact with each other. This can often be traced, in particular, in various transitional phenomena, one of which are adverbial equivalents of the word in the modern Ukrainian language – semantically coherent, but differently structured compounds that have the properties of the adverbial class of words.The most common formal structure of the adverbial equivalents of the word proves to be prepositional-case forms, for example, bez perestanu (without ceasing), do boliu (to pain), z (iz) zadovolenniam (with pleasure), nad miru (beyond measure), u (v) pechali (in sadness), etc. However, linguists have not yet distinguished prepositional-case forms of a syntactically free and semantically integral character.Purpose. The purpose of the article is to distinguish between syntactically free and semantically integral prepositional-case forms that transform into the class of adverbial equivalents of the word.Methods. The research employed the method of observing linguistic material, the transformational method, the method of contextual analysis, the method of modelling equivalents of the word developed by A. Luchyk, and the descriptive method.Results. Adverbial equivalents of the word reflect the second – prepositional (analytical) – degree of adverbialisation of the prepositional-case form when the semantic load of the case is lost, but the semantic load of the preposition is preserved. At the same time, within the limits of the prepositional-case forms of the prepositional adverbialization degree, there are those in which the preposition performs a function not inherent to it.The prepositional-case form can be extended by other dependent elements. In some cases, attributive or indicative units are located between the prepositional element and the substantive, which do not change the adverbial character of the prepositional-case form as a complex morpheme. In other cases, the prepositional- case form is extended by other postpositive units, which indicates the separate functioning of the prepositional and case morphemes.Discussion. Taking into account the semantic neutralization of the preposition and case in some types of prepositional-case forms, obviously, within the prepositional (analytical) degree of adverbialisation of the prepositional-case form, it is worth distinguishing the non-proper-prepositional degree, which will be represented by units called “equivalents of the word” by lexicologists. Accordingly, the prepositional-case forms of the first (prepositional-case) and second (prepositional) degrees of adverbialisation should be considered syntactically free, and the forms of the non-proper-prepositional degree of adverbialisation should be considered semantically integral. The most typical manifestations of semantically integral prepositional-case forms in modern Ukrainian are the structures of the models “bez – without + genitive case” (bez kintsia – without end, bez miry – without measure, bez vahan – without hesitation), “z (iz, zi) – with + instrumental case” (z (iz) zadovolenniam – with pleasure, z (iz) lehkistiu – with easiness, z oburenniam – with indignation), “u (v) – in + local case” (u (v) nespokoi – in restlessness, u (v) bentezi – in confusion, v ochikuvanni – in expectation).The perspective of the research is in a broader survey of lexical units that have a formal prepositional-case structure, in particular phraseological units. Similar explorations will make it possible to distinguish syntactic, morphological and semantic phenomena more clearly.