The paper is devoted to some problems of the stratification and analysis of Baltic loanwords in the Russian language, mainly on the basis of the early Baltisms. The substrate Baltic origin of such phenomena as аkanye, pleophony, as well as a long preservation and a consecutive preservation of reduced vowels remains unproved. The exceptional closeness of the Slavic and Baltic languages makes it difficult to identify substrate Baltic elements in the East Slavic dialects on the lexical level. The oldest strata of the Baltic elements in the vocabulary of Slavic languages are extremely difficult to be determined because of the lack of formal criteria for distinguishing them from their genetic counterparts. Theoretically many Russian (East Slavic) words treated as eastern dialecticisms of the Proto-Slavic language may also be determined as old Baltisms. The work at these problems is illustrated in the paper by the examples of Russian words, related both to the literary language and dialect vocabulary, as well as to the old Russian vocabulary.