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The reproductive outcomes of laboratory rats (Rattus norvegicus) housed at different distances (2, 20 and 80 m) from a predator (Lynx lynx) were investigated. Virgin female (n = 120) and m3ie (n = 40) rats of an outbred laboratory population were used for the experiments. Groups of rats (one male and three females) were housed in standard cages in close proximity to the predator Litter size, sex ratio. number of live pups, number of placental scars and corpora lurea were counted; and pre- and post-implantation losses were calculated for each female. The reproductive success of females, estimated as the number of live pups per female, was significantly higher in both control groups (20 and 80 m) than in both experimental Eraups (2 and 2 m). Equal numbers of corpora lutea in all groups but different numbers of placental scars between control and experimental groups indicated higher pre-implantation losses in the experimental groups. Post-implantation losses were also higher in both experimental groups. Total losses (calculated as a difference between the number of corpora lutea and live pups) were twice as high in experimental groups. Reproductive success of rats depended on concentrate/intensity of predator scents: when concentration/intensity was higher, the number of live pups was less and the total loss was higher.