In the public sector, immunization reminder/recall systems have been shown to increase return visits and therefore, enhance vaccine delivery. This study's primary objective was to measure the efficacy of reminder/recall systems (manual postcard or a computer generated phone message) in private provider offices through collection of return visits and vaccine delivery rates. Six private pediatric practices were selected to participate in the study based upon similar immunization delivery rates as determined through CASA (Clinic Assessment Software Application) assessments (range, 22-46%). Sites were randomly assigned to one of three arms of the study: mail, autodialer, or control. Study participants were children less than 12 months of age and eligible for first, second, or third DTP/DTaP. Enrollees were followed for up to thirty days after target immunization due date with return visit and vaccine delivery status recorded. Study site return visit rates for the six months prior to initiation of the intervention were determined to measure the effect of reminder/recall systems at each site. Through November 1997, 649 children were enrolled in the study. Results include data for 417/649 (65%) children who have completed the study. Distribution of children by study intervention are mail n=98, autodialer n=93, and control n=226. Return visit rates by intervention are mail 92%, autodialer 97%, and control 64%. Ninety percent of children with a return visit received the target DTP/DTaP. Comparisons of baseline return visit rates to intervention return visit rates will be updated at presentation. Preliminary analysis suggests a trend towards increasing return visit rates at intervention sites. Return visit rates at an autodialer site increased from 75% to 94% while return visit rates at a control site remained unchanged (58 to 61%). Our analyses suggest, that as in the public sector, reminder/recall systems likely enhance return visits in private pediatric offices.