The aim of this paper is, by using Computational linguistics method to analyse collocations of ethnonyms leiši and lietuvieši ‘Lithuanians’ in “Balanced Corpus of Modern Latvian” (Līdzsvarots mūsdienu latviešu valodas tekstu korpuss), compare contextual semantics of both ethnonyms. Comparing the frequency of use of the lexemes lietuvieši and leiši ‘Lithuanians’ in the modern Latvian language text corpus, the prevalence of the ethnonym lietuvieši is evident, therefore, the ethnonym leiši, regardless of its use as synonymic designation (sometimes in one and the same text), can be considered as an obsolete word. The desemantisation cases of the ethnonym leiši, detected in the corpus, show its oldness and varied functionality in Latvian language. The evidences to prove the statement of the “Modern Latvian Language Dictionary” (Mūsdienu latviešu valodas vārdnīca) that the lexeme leiši nowadays “carries slightly pejorative stylistically expressive colouring” were not found in the text corpus. In general, the image of a Lithuanian reflected in the modern Latvian language text corpus is rather positive – mostly in historical, language, culture and sports contexts, yet in the context of economics and emigration rather negative impression of Lithuanians is expressed.