P. M. Lewinsohn has theorized that depression is related to the amount of positive reinforcement that an individual receives. Lewinsohn has supported this model in adults by showing that depression is correlated with an increase in unpleasant activities and a decrease in pleasant activities. This study extended Lewinsohn's model by developing measures of children's mood-related activities. Subjects were children (166 boys and 156 girls), ranging in age from 8 to 12 years, who were enrolled in the public school system of a mid-sized midwestern city. Children identified, in 15-minute classroom sessions, 3 pleasant and 3 unpleasant activities. The types of activities reported differed across both age and sex. Common responses were included in the Pleasant Activities Survey and the Unpleasant Activities Survey. Several studies examined the relationship between children's activities and depression to test the generalization to children of Lewinsohn's reinforcement theory of depression. The study shows that children's mood-related activities can be reliably classified using a schema adapted for children from one originally used to classify adults' activities. One table and one figure illustrate the discussion. (Author/SLD)