Summary Under biodiversity investigations carried out by Ornithological Society at the local level, most valuable to nature unprotected areas were singled out in Rokiskis (21 territory), Pasvalys (11), Prienai (8), Raseiniai (7) and Kaunas (6) districts. Data on threatened species (plants, birds, mammals and certain insect groups) are presented and show a great potential value of such territories—most nature values in Middle Lithuania are situated outside the state preserves. The necessity for revision of the system of protected areas in the region is stressed in the article.