Seven patients operated on in a period of two consecutive days in the Havenziekenhuis, Rotterdam, the Netherlands developed symptoms of sepsis following a relatively minor procedure. One patient developed fever and hypotension a few hours after surgery, and developed thrombocytopenia and leucopenia. Postoperative bleeding occurred as a result of the thrombocytopenia, necessitating further surgery. This patient developed serious multi-organ failure, and required prolonged intensive care treatment. The other six patients developed less serious infections, the main symptoms of which were fever, leucopenia, thrombocytopenia and impairment of liver- and kidney function. They recovered quickly. Bacteriological investigation revealed that the infection was caused by extrinsic contamination of the intravenous anaesthetic propofol with Klebsiella pneumoniae and Serratia marcescens. Due to the high risk of contamination of the lipid formulation of this preparation, the use of propofol requires the following measures: syringes should be used just once; vials should be punctured just once; and administration should take place within 12 h after opening the vial or the ampoule. Hygienic working methods are also of crucial importance.