His research on Lithuanian personal names led him into the study of place-names. From these he was able to determine that the homeland of the Lithuanians and other Baltic peoples up to the 6th to 9th centuries CE had been just north of Ukraine in the area around the Pripyat River. In addition, he studied the chronological sequence of Slavicloanwords in the Baltic languages.
Kazimieras Būga, from the Encyclopedia Lituanica I-VI, Boston, 1970-1978, published in the Lithuanian Word by the Seimas Commission on Traditions and Heritage of Lituanistics