A concept for combined enteral and parenteral nutrition for critically ill patients is described in which endogenous substrate production during the acute phase of illness is taken into consideration and hyperalimentation is avoided. The nutritional goal is defined by multiplication of the base rate, i.e. body weight (BW) in kg as delivery rate in ml/h (wedge 24 kcal/kg BW/24 h), with a target factor, which varies between 0.2 and 1.8. An equivalent composition of enteral and parenteral nutrition allows a transition between both forms without problems. Simultaneously, immunologic aspects of nutrition are considered as well and both forms of nutrition are complemented by immune-modulating substrates such as glutamine and antioxidants.