Reported here are the microbiological and epidemiological details of a presumed outbreak of aerobic gram-negative bacilli infections affecting 19 hematological patients, which was traced to contaminated disinfectant. Over a 5-month period, the following organisms were isolated from the blood cultures of 19 neutropenic patients: Pseudomonas fluorescens (n = 13), Achromobacter xylosoxidans (n = 12), Comamonas testosteroni (n = 2) or Stenotrophomonas maltophilia (n = 1). The affected patients were all treated with an expensive regimen of broad-spectrum antibiotic therapy. The same bacteria were recovered from environmental samples as well as from the water pipes of an apparatus for dispensing disinfectant (didecyldimethylammonium chloride). Genotyping results indicated that many of the clinical strains were identical to strains isolated from the apparatus. It was eventually discovered that the night staff was in the habit of disinfecting the blood-culture bottles before use, thereby contaminating the bottles with bacteria contained in the disinfectant. Contamination of the apparatus resulted from faulty maintenance.