The goal of this report is to find out whether early exposure of mice to the open-field results in altered behavior of the same adult mice in the same open-field. Early exposure to the open-field was carried out between birth and weaning; two control groups were included: control 2 (mice exposed to a reduced dark space) and control 1 (mice left undisturbed). The (male and female) mice were of the Balb/c and C57Bl/6 strains. Adult C57Bl/6 female mice of the openfield and control 2 groups ambulated to the same extent in the periphery of the open-field, and mice of both groups ambulated more than mice of the control 1 group; no consistent difference between the three groups was noticed on defecation, or ambulation in the center of the field. No effects of early exposure to the open-field were observed in mice of the Balb/c strain. The effect of early exposure to the open-field, or to a dark space, on adult behavior depends on the murine strain, on sex, and on the behavior measured.