Between January and June 1976, eight cases of primary bacteremia due to Enterobacter cloacae occurred in patients after open-heart surgery in a hospital in Connecticut. Epidemiologic studies implicated radial arterial catheters as the route of acquistion of E cloacae, and bacteriologic studies confirmed arterial pressure transducers as the sources of bacteria. Prospective studies indicated that the disposable domes from the pressure transducers did not prevent the spread of bacteria from contaminated transducers to the arterial catheters. This is the first report of transducer-acquired bacteremic infections occurring with the use of disposable domes. Although disposable domes may decrease the chances of cross-contamination of circuits for monitoring pressure, they do not, as previously thought, eliminate the risk of bacteremia from this source.