The study of oral spontaneous speech in any language is impossible without reference to its elements which are usually considered by traditional linguistics to be ‘negative' material. Analysis of such speech failures committed by native speakers of the Russian language seems necessary in order to get the most complete picture of the current state of the spoken language and, accordingly, the language in the native speaker's representation. The article analyzes slips of the tongue relating to different levels of language (phonetic, lexical, grammatical), identifies possible reasons for their occurrence. The study was conducted on the basis of two corpuses of oral speech: the corpus of everyday Russian speech ‘One Speaker's Day' (ORD, mainly dialogues and polylogues) and a block of speech of physicians from the ‘Balanced Annotated Text Library' (exclusively monologues). The users' subcorpus includes 250 units in contexts and is strictly balanced by the ratio of dialogical and monological texts (126 and 124 respectively). Thus, the present study is based on materials that currently most fully and adequately reflect the specific features of oral spontaneous speech in its living manifestation, both monological and dialogical / polylogical. In addition, due to the specific nature of the corpuses used as sources, some conclusions are made about the frequency of the appearance of slips of the tongue in monologues and dialogues separately. This juxtaposition of the two forms of living speech is a significant factor, influencing the appearance of slips of the tongue in different ways. Analysis of the material showed that in a monologue a person makes mistakes more often. Most likely, this is due to the specific features of experimental speech (speech with a visible voice recorder in front of the speaker), which is definitely less natural than everyday communication of the ORD informants.