A race of clothes lice adapted to feeding on rabbits is kept at a laboratory longer than 50 years. For this period, more than 850 insect generations undergoing no change in a number of biological tests and morphological indices have been obtained. They have retained a high susceptibility to Provacheck rickettsia infection. All infected lice die, partially with the signs of hemolytic imbibition. Their rickettsial accumulation is as high as 10(5.0) ID50 per insect for albino rats.