On a routine sterility check, the authors found bacteria in their vitrectomy machine. Serratia marcescens was detected in the pressure receiver of a roller pump vitrectomy machine. The authors improved the machine by installing a millipore filter in front of the receiver that prevents bacteria from entering it without interfering with the pressure measurements. The origin of Serratia was probably a patient with endophthalmitis who was operated on long before the routine check. Although this appears to be the first report of a bacterial contamination of a vitrectomy machine, the results of testing show that this situation is indeed possible. The authors strongly recommend routine checks of the equipment and suggest mounting an antibacterial filter.