Rationale: Obesity is an increasing health risk worldwide, with the USA recording prevalence in adults of around 20%. The mean body weight of obese patients is also increasing. One of the strategies to treat extreme obesity (Body Mass Index (BMI) > 40 kg/m2) is weight-reducing surgery like laparoscopic gastric banding or gastric bypass. During anaesthesia, morbidly obese patients are exposed to an increased risk at developing postoperative wound infections, apnoea and thrombotic events and may be more difficult to intubate. Routinely, amongst others, cefazolin, morphine, nadroparin and atracurium are administered in standard dosages. However, it is not known to what extend the pharmacokinetics and/or -dynamics of these drugs are affected in morbidly obese patients. Therefore, evidence-based dosing schedules for these drugs in morbidly obese patients should be developed.