Observations were carried out in three breeding complexes to study the conditions under which rodents invaded the premises of pigs. The species composition of the rodents was determined through making use of biometric data. The number of rodents was established via the method of the 'trap-per-24 hr periods', the inquiry-visual method, and the method of the powdered plots. With the use of the 'visual' method at 4 hr intervals the rhythm was found of the activity of rodents as well as the habitats preferred by them. It was established that in all three swine breeding complexes the most active movement at night was at 22.00. The canalization and shafts were shown to be one of the basic ways for rodents to invade the barns, storage-houses, and halls. The wide slits of the grates and fans without nets also contributed to rodent invasion. The conclusion was drawn that with the building patterns used in the swine breeding complexes there were conditions that rendered possible the establishment of habitats in them. Suggested is the working out of normative parameters concerning the rat invasion.