This study investigated behavioral differences between neonatal rats with vasopressin AVP deficiency (di/di) and those with little (+/di) or no deficiency (+/+) using a number of open field metrics. Infant rats (pups) at days 7 and 10 postpartum were videotaped in individual and group trials in a temperature-controlled arena for 12min. Pups were tracked every 5s for tip-of-the-nose and base-of-the-tail coordinate positions. These positional data were transformed, using computer algorithms, into measures of activity, change in orientation, distance moved, cells occupied, wall contact, number of corners visited, and degree of aggregation. Analysis of these data revealed some phenotypic differences among genotypes for 7-day-old pups in individual trials, but there was no clear pattern of genotypic differences. By day 10, however, there were dramatic differences. AVP deficient pups differed significantly from both +/+ and +/di pups on most individual and group metrics. As measured by effect size, group effects were especially large. The behavioral results were consistent with previous findings in adult di/di rats and indicated that 10-day-old di/di pups were hyperactive and had social deficits. AVP deficient pups also appeared to have accelerated locomotor development and to exhibit stereotypic behavior. These results suggest that Brattleboro, di/di, pups are a potentially important animal model for investigating the role of AVP in early locomoter and social development. These behavioral metrics are generalizable to infants of other rodent species and thus may allow early behavioral phenotyping and the assessment of behavioral deficits.