This study examined the effect of Parent Child Interaction Therapy (PCIT) on Head Start families whose children were at risk for later conduct disorders. The study also served as a screen for behavior problems in Head Start children. Data was collected on Head Start families receiving standard care and compared to families receiving PCIT in addition to standard care. It was hypothesized that, compared to the families receiving standard care, the study group receiving standard care and PCIT intervention would have (1) children with fewer behavior problems, (2) children who are more compliant to parents' commands, (3) more positive and effective parent-child interactions, and (4) lower parental stress and depression levels and higher family support. The study was comprised of three phases, using a battery of quantitative standardized assessments completed by teachers, parents and children. In Phase I parents of Head Start children in Alachua County, FL were asked to complete the Eyberg Child Behavior Inventory and a Demographic Data Sheet in order to determine the prevalence of child behavior problems. There were approximately 800 children in Head Start in Alachua County at the time of the study. Phase 2 included participation by parents and teachers of 100 3-year-old and 100 4-year-old Head Start children who were randomly selected from Phase I. Head Start child and parent functioning were measured to provide normative data using standardized assessments from the parents and teachers. Phase 3 included 30 Head Start children with problem behavior in the clinical range, with at least one parent able to participate in treatment. In Phase 3, families were randomly assigned to standard care or PCIT groups (half in each) and were not informed of the assignment until after the pre-assessment protocol. Data in this phase was collected using standardized tests from parents, teachers, children, and observers before and after the PCIT intervention and at a four-month follow-up. Treatment outcomes of PCIT were determined at post-treatment, and the maintenance of PCIT gains were assessed four months later. PCIT did not end until the treatment goals were attained. Treatment effects were evaluated by comparing the standard care group and the standard care plus PCIT group on all of the dependent variables.