Chloramphenicol treatment, today the therapy of choice against typhoid fever and other Salmonella infections, is often inadequate in that relapses are common,1-3the organisms persist in bile or stools for variable periods of time, carrier states may not be permanently eradicated, and the important complications of intestinal hemorrhage and perforation still may occur.4The use of an additional antibiotic against Salmonella infections, so that the dose of each drug might be decreased and the efficacy increased, therefore appeared to us to be a logical approach to more adequate treatment. The choice of such an additional drug would depend upon the sensitivity of salmonellae to combinations of the available antibiotics. To assist in selection of such an antibiotic combination, many methods are available. One is that of clinical trial. Another is that of in vitro testing; commonly, the serial tube dilution and plating method.5,6This latter technique is