E nhancement of functional recovery during the subacute and chronic phases of stroke represents a major therapeutic goal because a significant proportion of patients have persisting neurological deficits, even with optimal acute care and conventional rehabilitation. Preclinical in vivo models suggest that a time-limited window of neuroplasticity opens after stroke.1 New therapeutic approaches that stimulate these repair mechanisms may be able to exploit this opportunity, and a range of these is currently under investigation, including small molecules that target specific processes, small molecules that have a general stimulatory effect that may aid rehabilitation, growth factors, cell therapies, and physical modulation of neuronal networks.2 The Ï-1 receptor chaperone protein (Sig-1R) mediated functional recovery in a model of neuronal plasticity relevant to stroke.3 Sig-1Rs mainly reside in the endoplasmic reticulum and are enriched in the mitochondriaassociated endoplasmic reticulum membrane but can change their intracellular location in response to cellular stress. 4 The biochemical function of the Sig-1R is that of a molecular chaperone, stabilizing proteins in response to cellular stress 5 Background and Purpose-The Ï-1 receptor (Sig-1R) agonist cutamesine (SA4503) enhanced functional recovery after experimental stroke with a treatment initiation window of 48 hours and chronic treatment for 28 days. We conducted a phase 2 clinical trial exploring the safety, tolerability, dose range, and functional effects of cutamesine in patients with ischemic stroke. Methods-Subjects were randomized between 48 and 72 hours after stroke to receive cutamesine 1 mg/d, 3 mg/d, or placebo for 28 days. Effects on safety and function were assessed at baseline, at end of treatment (day 28), and at end of followup (day 56). Results-In 60 patients, treatment with both cutamesine dosages was safe and well tolerated without significant differences in numbers of treatment emergent or serious adverse events. No significant effect was observed on the primary efficacy measure (change in National Institutes of Health Stroke Scale from baseline to day 56) or modified Rankin Scale and Barthel Index scores. Post hoc analysis of moderately and severely affected patients (baseline National Institutes of Health Stroke Scale, â„7 and â„10) showed greater National Institutes of Health Stroke Scale improvements in the 3 mg/d cutamesine group when compared with placebo (P=0.034 and P=0.038, respectively). A trend toward a higher proportion being able to complete a 10m timed walk was observed for cutamesine-treated subjects. Conclusions-Cutamesine was safe and well tolerated at both dosage levels. Although no significant effects on functional end points were seen in the population as a whole, greater improvement in National Institutes of Health Stroke Scale scores among patients with greater pretreatment deficits seen in post hoc analysis warrants further investigation. Additional studies should focus on the patient population with moderate-to-severe...