The whole concept of bioequivalence is based upon the existence of a clear relationship between drug concentration and clinical effect. To date there are insufficient data available in the form of publications to support this concept. Both the pharmaceutical industry and the regulatory authorities could do more to promote this issue and publish relevant information. The pharmaceutical industry could provide more information on concentration-effect relationships in volunteers and patients. Upon expiry of the patent, regulators could provide estimates of the inter- and intra-subject variability in the pharmacokinetics of a drug in volunteers and patients, assessment of therapeutic windows for drugs and drug classes and their impact on bioequivalence acceptance criteria. Current regulatory guidelines refer to rate and extent of absorption BUT there is no rate parameter which allows products to be compared for both pharmaceutical quality and safety and efficacy.