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Background: Objective adherence measures are of increasing interest in antiretroviral treatment (ART) monitoring. Hair ART levels predict virologic suppression, and hair is easy to collect and store. No previous study has examined hair levels in an India-based cohort or laboratory. Methods: Small hair samples were collected from HIV-positive participants on either efavirenz (EFV)-based or nevirapine (NVP)-based ART in a South India–based study. Hair samples were split and analyzed for EFV or NVP in the University of California, San Francisco –based Hair Analytical Laboratory and the analytic laboratory of the Division of Nutrition at St. John's Research Institute, Bangalore, India, using liquid chromatography/tandem mass spectrometry. Agreement (using Bland–Altman methods) and rank correlation between the 2 laboratories' hair levels were calculated. Rank correlation between self-reported adherence (SRA) over the previous month using a visual analog scale and hair ART levels was calculated. Results: Among 75 participants (38 on NVP; 37 on EFV), the correlation between NVP levels generated by the 2 laboratories was 0.66 (P < 0.0001) and between EFV levels was 0.87 (P < 0.0001). Measurements from St. John's Research Institute were usually within 20% of those from the University of California, San Francisco Hair Analytical Laboratory. SRA was essentially uncorrelated with hair antiretroviral levels for either drug (all correlations < 0.04). Hair levels showed variability in adherence although SRA was >85% in all participants. Conclusions: Hair ART levels measured by both an India-based laboratory and the standard U.S.-based laboratory showed generally high agreement and correlation, demonstrating local capacity. As in many other cohorts, hair ART levels and SRA were not well-correlated, likely indicating limitations in self-report and the need for objective adherence monitoring in resource-limited settings. [ABSTRACT FROM AUTHOR]