The animals' reactivity and the levels of experimental anxiety during pregnancy and lactation in female rats were studied using the burying behavior test. The three main parameters analyzed in this test were: the cumulative burying behavior, the burying behavior latency, and the number of shocks necessary for displaying the behavior. The burying behavior was studied at the 7th, 14th, and 21st days of pregnancy and lactation. An additional group tested 12 h after parturition was also included. Simultaneously, in all animals, the ambulatory behavior was evaluated. All results were compared with those obtained in a control group of ovariectomized females. At the end of pregnancy a clear increase in burying behavior latency accompanied by a decrease in cumulative burying behavior was observed. Similarly, a clear reduction in burying behavior immediately after parturition was found. The number of shocks necessary for displaying the burying behavior were not modified along pregnancy and lactation with the exception of a clear decrease for the 7th lactation day. Changes in locomotor activity were observed at pregnancy, but not along lactation. These changes do not account for the reduction in burying behavior observed at the 14th gestation day. Data related to the reduction in burying behavior observed during gestation are discussed on the possible participation of progestins, while those found during lactation are discussed on the bases of the variations in serotonin and beta-endorphins that normally occur during this period.