The language of the 18th century Catholic writings is given a negative assessment in nearly all the works devoted to the history of the written Lithuanian language. The main reason of such evaluation is a great number of Slavisms found in them. Researchers usually present lists of such loanwords. In this study these lists were reviewed and collated with the lexis of the authors of the 16th and 17th centuries. A more detailed analysis of the Slavisms showed that about 90 per cent of these borrowings had been used by the authors of the two previous centuries. A comparison of the two editions of 'Broma atwerta ing wiecznasti' by M. Alsauskas (in 1753 and 1759) revealed that the loanwords of the first edition were replaced by Lithuanian words in 94 cases in the second edition and a reverse substitution was observed only in four cases. This situation leads to the conclusion that the underlying reason for this prolific use of Slavisms was not merely the spread of the Polish language and the denationalization of the Lithuanian clergy. The author of this article is inclined to believe that a significant factor could have been the desire of the authors of Lithuanian writings to create a church style differing from the spoken everyday language. To this end the eighteenth-century writers profusely used Polish words only adapting them to the rules of Lithuanian grammar.