The hypothalamic-pituitary-adrenal axis mediates the response to stressors in many higher organisms. A well-regulated response is critical for adaptation and survival. Accurate measurement of stress is a fundamental requirement for studying both behavioral reactions and molecular mechanisms of stress response.    We make tools to measure the primary stress-associated molecules mediating HPA axis activity. Our glucocorticoid assays help monitor stress response more efficiently in as little as 1 µL of plasma without extraction.