A microbiological quality control study of parenteral nutrition (PN) is presented. The study was carried out in the Pharmacy and Microbiology Services of the Hospital de la Santa Creu i Sant Pau (Barcelona, Spain) from April 1991 to May 1998 and represents more than 25,000 lipid-containing PN admixtures prepared during that 7-year period. A randomized sampling procedure according to the cumulative sum control charts was performed and a 0.45-microm membrane filtration method was used as the microbiological test. Validation showed that the method is sensitive for sterility tests. Bacterial growth was observed on 59 filters (4.58% of the samples). A second control was made for these positive outcomes, and bacterial growth was found in only two cases. The patients' clinical history was reviewed and no relation between the microorganisms of the nutrition and the results obtained from blood cultures was observed. The quality control study revealed a low incidence of contamination in our PN preparation process.