The proposed experiment will examine the effects of handling the pups, and of intrusions into the nest for cleaning, on the behavior of mouse mothers and pups. Ethologically relevant variables will be measured by use of a dual-chambered cage fashioned such that the mother can be either allowed into or excluded from entry into the second chamber. Behaviors to be studied include traditional measures of maternal behavior (e.g., licking, retrieving, scattering pups), movement of the nest between chambers, invasions of non-parental space by pups, and open field behavior of the offspring at maturity. It is hypothesized that: 1) Handling will speed the invasion of non-parental space, and use of food and objects in that space, by pups. 2) Invasion of non-parental space, which has ethological relevance in respect to dispersion, will be related to maturation and adult open field exploration. 3) Handling and intrusions will increase between-chamber movements of the nest by the mothers. 4) Nest moves and other measures of maternal behavior will correlate with the pups' later invasion of non-parental space and adult open field exploration.