The detergent-resistance properties of 208 independent isolates of the Enterobacteriaceae have been examined. Of these bacterial strains, 200 were able to grow in the presence of greater than or equal to 5% sodium dodecyl sulfate, including all members of the Klebsielleae tribe. This resistance does not appear to be plasmid encoded. It is proposed that detergent-resistant organisms be termed saponotolerant or saponophilic, by analogy with other microorganisms occupying harsh ecological niches. In contrast to their prevalent resistance to anionic detergents, not one of the 208 strains tested was found to grow in the presence of three different cationic detergents. This sensitivity to cationic detergents may be of significance in combating nosocomial infections.