The source of coagulase-negative staphylococci (CNS) isolated from blood cultures and thought to be contaminants was investigated over a two month period. Isolates recovered from swabs taken from patients, doctors and laboratory staff were compared with the blood culture patient isolate in an attempt to identify the source of contamination. Six hundred and ninety-six blood culture sets were received of which 28 were contaminated with CNS. Nineteen of these blood cultures had sufficient data to be included in this study. Six were matched to isolates from the patient's skin and none to the medical or laboratory staff. Major differences in the antibiograms were seen between the patients, medical and laboratory staff. Organisms from patients and medical staff were more likely to have multiple antibiotic resistances. It appears that the most important source of CNS contamination of blood cultures processed in a semi-automated manner is the patient's own skin flora.