The purpose of this study was to develop an animal model for behavioral features of type II, early-onset alcohol abuse. To perform this research, cerebrospinal fluid (CSF) monoamine metabolite concentrations and home-cage social behaviors of 29 rhesus macaque subjects were examined in a 4-year longitudinal study. Half of the monkeys were reared for their first 6 months with their mothers, and the other half were reared without adults, instead with access only to monkeys of similar age. When the subjects were 6 months old, and again when they were 50 months old, they underwent a series of four, 4-day social separations. We obtained cisternal CSF before and during the first and last separation of each series to quantify 5-hydroxyindoleacetic acid (5-HIAA), 3-methoxy-4-hydroxyphenylgycol (MHPG), and homovanillic acid concentrations. After the 6-month separations, subjects were placed into social groups, and social dominance rankings were assessed. Before and after the 50-month separations, social dominance rankings were evaluated again, and home-cage aggression and social behavior data were collected. Over the 3 1/2 years between CSF samplings, records were maintained of subjects' removal from their social groups for excessive aggression or treatment for wounding. Our results showed that among infants, reduced CSF 5-HIAA was correlated with low social dominance. As young adults, subjects from both rearing groups with low CSF 5-HIAA and MHPG concentrations exhibited reduced rates of social interaction and low social dominance rankings. In addition, peer-reared subjects with low CSF 5-HIAA concentrations exhibited inept social behaviors, and were frequently removed from their social groups for excessive aggression and deviant social behaviors. From these results, we conclude that the peer-rearing paradigm aggravates the untoward social consequences associated with low CSF 5-HIAA concentrations over and beyond reducing CSF 5-HIAA concentrations, suggesting that early experiences may contribute to CNS serotonin changes that increase the disposition to type II-related behaviors.