The effectiveness of home-based early behavioral interventions for children (2:6-4:0 years old) with autistic spectrum disorders was studied over 9-10 months. Measures of autistic severity, intellectual, educational, and adaptive behavioral functioning were taken. There was no evidence of recovery from autism. High-intensity behavioral approaches (mean 30 h/week) produced greater gains than low-intensity programs (mean 12 h/week). Lovaas- and complete application of behavior analysis to schools approach-type interventions produced largest gains [similar to gains produced by longer-term clinic-based applied behavior analysis (ABA) programs]. Within the high-intensity groups, increased temporal input on the program was not associated with increased gains in the children. The results from clinic-based ABA trials were partially replicated on a home-based sample, using children with greater autistic and intellectual impairments.