We studied the consequences of keeping in isolation (1 animal per cage) during the puberty period of female rats born from intact mothers or from mothers suffering an 1-hour immobilization stress in the last trimester of pregnancy, and its influence on oestrous cycle and anxiety level of the adult offspring. There were no changes in the rates of anxiety level depending on oestrous cycle phase among both control and prenatally stressed females in isolation. On rats moving to the groups (4-5 animals per cage) the control rats unlike the prenatally stressed individuals show this dependence. About 50 % of the control and experimental rats, grown in isolation, are characterized by reduction ofoestrous cycle duration (3.3 +/- 0.05 days). The rest of the animals have the normal duration ofoestrous cycle (4 +/- 0.3 days), or prolonged duration (5 +/- 0.25 days). The control rat's oestrous cycle increased because ofdioestrus phase, whereas prenatally stressed rats oestrous cycle increased because of estrus phase. On females moving to groups the estrous cycle duration of most rats increased, but among the prenatally stressed rats there were still females with prolonged estrus phase. Besides, the prenatally stressed rats moved from isolation to groups has the reduced blood level of corticosteroid, and the control rats has an increased one. According to our opinion, under the conditions of low population density the prenatal stressed animals show better adaptive reaction because the estrous cycle reduction and the estrus phase prolongation make the possibility of pregnancy higher.