BAU, Bioequivalent Allergy Unit. A potency unit used to characterize biological activity of select standardized allergen extracts. BAU was defined using skin prick test titrations in a sensitized patient population. Reference standards were then established by the FDA and utilized by extract manufacturers to maintain the defined relative potency for the specific, standardized extract. This standardization process reduces variability in potency from lot to lot. Standardized grass (e.g., Timothy, Sweet Vernal, Bermuda, etc.) and cat are labelled as BAU extracts.