Observations of reduced utilization of alcohol and drug abuse treatment following the introduction of managed behavioral health care suggest that substance abuse services may be especially responsive to managed care restrictions and limits. In publicly funded treatment systems, patient attributes, system and provider characteristics, and financing mechanisms may heighten susceptibility to unintended effects. The State Substance Abuse and Mental Health Treatment Managed Care Evaluation Program reviewed state managed care programs for publicly funded alcohol and drug treatment services and is evaluating programs in Arizona, Iowa, Maryland, and Nebraska. The article describes initiatives and outlines evaluation activities. It discusses the opportunities and challenges of assessing public managed care plans.