Chlorhexidine degradation by clinical isolates such as Pseudomonas aeruginosa, Pseudomonas cepacia, Alcaligenes faecalis, Alcaligenes xylosoxidans, Serratia marcescens and Pseudomonas sp. strain No. A-3 (as a control organism) was investigated after enrichment with chlorhexidine. By this enrichment, P. aeruginosa (Nos. 1-3), A. faecalis, A. xylosoxidans (No.2) and S. marcescens IFO 3046 smoothly acquired resistance to a high concentration of chlorhexidine. Among them, only S. marcescens IFO 3046 showed the same degradation pattern as the control organism, which degraded chlorhexidine via a modified degradation pathway. The other strains were thought to have a different resistance system from that of Pseudomonas sp. strain No. A-3 and S. marcescens IFO 3046.