Higher levels of the inflammatory biomarker interleukin-6 (IL-6) correlate with poor clinical outcome in acute ischemic stroke (AIS). Minocycline (MC) is a known anti-inflammatory agent; thus, the effect of MC on IL-6 in the first 24 h of AIS was investigated to determine potential anti-inflammatory activity. The Minocycline to Improve Neurologic Outcome in Stroke (MINOS) study was a non-randomized dose-escalation (3.0-10.0 mg/kg) trial of IV MC for AIS within 6 h of onset. Plasma IL-6 samples were collected prior to MC treatment at 1, 24, and 72 h and compared to those collected in a separate observational study of blood biomarkers in AIS. IL-6 levels were measured by commercially available ELISA kits. The lower limit of detection for IL-6 was 1 pg/ml. Sixty MINOS subjects and 29 non-MINOS subjects were enrolled, and there was no difference in baseline stroke severity. There was no significant difference in IL-6 level pre-MC treatment at 1, 24, or 72 h. However, the odds of a non-detectable IL-6 at 24 h in MINOS were 8.94 (95% CI 2.62-30.46) compared with non-MINOS subjects. It is likely that even low doses of MC have a potent systemic anti-inflammatory effect in AIS. Whether this results in improved outcome will be tested in a randomized clinical trial.