ENThe author of the article presents some results of his current research and publishing project, financed by the Lithuanian Council of Science (Finance Contract no. LIT-8-83). Aim of the project is to publish, commenting on and interpreting a book of Jonas Šliūpas "Lithuanians in Relation to the Poles" published by him in Polish in New York in 1887. In 1889 this book has been critically reviewed by Jan Witort in "Przegląd Literacki" literary appendix to the St. Petersburg Polish weekly "Kraj". These two texts (one from J. Šliūpas, another from J. Witort) are interesting as historical sources. Translation into Lithuanian of texts is planned.