The susceptibility of Yersinia pseudotuberculosis, Y. enzerocolitica, Yersinia-like organisms and atypical strains of Yersinia against gentamicin, streptomycin, sulphamethoxazole, trimethoprim, trimethoprim-sulphamethoxazole, chloramphenicol, tetracycline, doxycycline, ceftriaxone, ceftazidime, moxalactam and n-f-thienamycin has been studied. All the 167 strains tested were highly sensitive to ceftriaxone, ceftazidime, moxalactam and n-f-thienamycin (MIC ≤ 0·5 mg/l). There were no strains resistant to gentamicin, trimethoprim and the combination of trimethoprim-sulphamethoxazole. There were 17·5% sulphamethoxazole and 16 streptomycin resistant strains among Y. enierocolitica and all the streptomycin resistant strains were resistant to sulphamethoxazole. There appears to be cross resistance as 22 of the 23 sulphamethoxazole resistant strains were also streptomycin-resistant. Therefore, sulphamethoxazole and streptomycin cannot be recommended for the empiric treatment of Y. enierocolitica infections.