BACKGROUND: Treatment with nucleoside reverse-transcriptase inhibitors (NRTIs) is associated with hyperlactatemia, presumably as a result of NRTI-induced mitochondrial toxicity. We examined the association of NRTI treatment duration and lactate level in human immunodeficiency virus (HIV)-infected patients and assessed the relationship of treatment duration and lactate level with insulin resistance. METHODS: Fasting arterialized venous lactate levels, routine blood chemistry findings, insulin resistance (determined by homeostasis model assessment [HOMA-IR]), percentage of body fat (determined by dual-energy radiographic absorptiometry), and detailed histories of antiretroviral therapy were obtained for 95 HIV-infected individuals. The independent association of NRTI treatment duration and lactate level was examined using multivariable linear regression. RESULTS: Among 95 subjects with a mean age (+/- standard deviation [SD]) of 44 +/- 8 years), 95% had NRTI exposure, with current NRTI use in 83%. The mean (+/- SD) lactate level was 1.24 +/- 0.46 mmol/L (6% had a lactate level > 2 mmol/L). Longer duration of NRTI use was positively associated with lactate level (beta = 0.047; P < .01), as were age, duration of protease inhibitor treatment, and HOMA-IR. Female sex and percentage of body fat were negatively associated with lactate level. After adjustment for age, sex, diabetes, percentage of body fat, and duration of protease inhibitor therapy, an increased duration of NRTI therapy remained significantly associated with lactate level (beta = 0.035; P = .04). However, the addition of HOMA-IR to the adjusted model attenuated the relation between duration of NRTI therapy and lactate level (beta = 0.024; P = .14), whereas HOMA-IR was significantly associated with lactate level (beta = 0.206; P < .01). Furthermore, HOMA-IR was also associated with NRTI treatment duration in adjusted analyses. CONCLUSION: NRTI treatment duration was independently associated with higher lactate level, but this relationship was attenuated after adjusting for HOMA-IR. These data raise the possibility that insulin resistance may be an additional mechanism through which NRTI therapy is related to lactate level.