It was hypothesized that node-link mapping a tool for visually representing client issues during drug abuse counseling, would reduce communication barriers between counselors and their African American and Mexican American clients. Three hundred twenty daily opioid users participated in methadone maintenance treatment programs in three cities for 6 months or longer following random assignments to mapping-enhanced or standard counseling. Clients in the mapping condition had fewer drug-positive urines (with respect to opiates and cocaine), missed fewer scheduled counseling sessions, and were rated more positively by their counselors on rapport, motivation, and self-confidence during the first 6 months of treatment. Significant interactions involving ethnicity and counseling condition suggested that mapping is more effective for African Americans and Mexican Americans than for Whites. The use of mapping appears to help reduce cultural, racial, and class communication barriers by providing a visual supplement and a common language that enhances counselor-client interchanges.