From Nov. 15 to Dec. 17, 1977, Pseudomonas cepacia was isolated from the blood of 16 patients in Odense, Denmark, and Nijmegen, Holland, 2--5 days after an operation with general anaesthesia. The fever started 14--70 h after operation and lasted 2--4 days. All patients recovered. 14/15 patients examined 7--51 days later had agglutinating antibody titres of 400-3,200 against the epidemic strain. Ps. cepacia with identical biochemical characters and sensitivity pattern was isolated from unbroken vials containing the anaesthetic fentanyl, which had been given to all 16 patients. Two batches were contaminated, one heavily so (10(4)--10(5) cfu/0.1 ml). Seven other batches examined yielded no growth. The preservative added to the vials was a mixture of methyl- and propyl-p-hydroxybenzoates which not only allowed growth of the Ps. cepacia strain but could also serve as a carbon source as did citric and malonic acids. The concentration of preservative was not reduced in contaminated vials. The vials had not been sterilized after closure; too much reliance had been placed on an aseptic technique and insufficient preservatives.