The Substance Abuse Mental Health Services Administration has promoted HIV testing and counseling as an evidence-based practice. Nevertheless, adoption of HIV testing in substance abuse treatment programs has been slow. This article describes the experience of a substance abuse treatment agency where, following participation in a clinical trial, the agency implemented an HIV testing and counseling program. During the trial, a post-trial pilot, and early implementation the agency identified challenges and developed strategies to overcome barriers to adoption of the intervention. Their experience may be instructive for other treatment providers seeking to implement an HIV testing program. Lessons learned encompassed the observed acceptability of testing and counseling to clients, the importance of a "champion" and staff buy-in, the necessity of multiple levels of community and agency support and collaboration, the ability to streamline staff training, the need for a clear chain of command, the need to develop program specific strategies, and the requirement for sufficient funding. An examination of costs indicated that some staff time may not be adequately reimbursed by funding sources for activities such as adapting the intervention, start-up training, ongoing supervision and quality assurance, and overhead costs. (Contains 3 tables.)