The advantage of animal studies is to study a relatively homogeneous group of animals instead of a heterogeneous group of patients in clinical studies. Animal studies also offer a wider range of possibilities for example such as examining toxicity of a specific treatment or studying the underlying mechanisms of diseases. However, because most of new therapies shown to be effective in animal studies have been ineffective in clinical trials, some guidelines including the Stroke Therapy Academic Industry Roundtable (STAIR) were proposed to improve the quality and reproducibility of individual animal studies evaluating neuroprotective drugs in ischemic stroke [1–3]. Recent special issues BChallenges and Controversies in Translational Stroke Research, Part 1 and 2^ in this journal provide an excellent overview as to the innate biological variability and the methodological challenges that are needed to address bias in preclinical research for the successful translation of experimental therapies to clinical stroke treatments. The proposed standards include (1) clinical relevance of animal models (detailed information on animals used (species, strain, age, weight, gender, etc.), selection of anesthetics, inclusion and exclusion criteria),(2) sample size calculation and accurate statistical analysis,(3) treatment (randomization, allocation concealment, dose-response determinations, therapeutic time window, blood-brain barrier permeability and tissue drug levels, physiological monitoring),(4) outcome (blinded assessment, at least two outcome measures (morphology and function), covering both acute (1–3 days) and longterm (7–30 days) endpoints), and (5) reporting of animals excluded from analysis, potential conflicts of interest, and study funding [1–7]. In addition, several challenges exist to successfully translate the outcomes from animal research to humans in a clinical setting. First, age and sex are two important non-modifiable risk factors for stroke [5, 8]. With aging, there is a shift toward a proinflammatory phenotype in the brain as well as the periphery, and blood-brain barrier disruption [8]. Women are protected from stroke before menopause, but have increased stroke rates and worse outcomes at older ages [5]. On the other hand, the use of adult reproductive female animals in stroke research is complicated by the sex hormone cycle. However, the male-biased use of research animals is distinguished from the clinical situation where there is a disproportionate and growing female stroke population, making it important to include both sexes with diverse ages in preclinical as well as clinical studies that evaluate potential stroke therapies. Second, cerebrovascular anatomy and collaterals, as well as biological and secondary neuroinflammatory responses to insults, are different between species or strains, causing flawed design, unreliable outcomes, unnecessarily more costs, and experimental animals [7, 9–11]. Genetic differences between animals and humans, and even within animal species, strains, and cell lines, may affect the immune responses and outcomes [10, 12, 13]. Third, stroke patients have many comorbidities or vascular risk factors including hypertension, diabetes mellitus, dyslipidemia, cardiac diseases, current smoking, obesity, poor diet, inactivity, high alcohol intake, psychosocial stress and depression, social factors such as marital and residence status (ie, living alone), and prestroke dysfunction, causing stroke severity [5, 14]. Animal models having these factors are also subjected to different stroke injuries or changes in the structure of the neurovascular unit [14]. Thus, the use of young healthy animals causes a barrier for translation of findings …