Drug development from phase I to IV usually takes place in adult patients. Sometimes drugs are especially designed for special patient groups and then research takes place in those groups. However, many drugs that are investigated in adults will be used at both ends of the human spectrum, from early neonates to the very old and in pregnant women. Usually pharmacokinetics and pharmacodynamics are highly different with sometimes unexpected side effects, and this leads to gaps in our knowledge how to use these drugs optimally and safely in these special groups. In this session examples of drug studies aiming at filling in these knowledge gaps will be presented.