Ninety-six urine samples were collected by a sterile technique from 75 dogs affected with urinary tract disease (cystitis, urolithiasis, prostatitis, etc) involving bacteruria. The infecting organisms were isolated and tested against sensitivity discs (penicillin G, streptomycin, chloramphenicol, tetracycline, sulphamethoxazole/trimethaprin and Sulphatriad). The commonest isolate was Escherichia coli, which was generally sensitive to several agents, though in eight cases it was resistant to all drugs. Next in order were Streptococcus faecalis, Staphylococcus epidermidis and Proteus spp. A double infection was present in 11 cases. Further data give a breakdown for sex and the clinical diagnosis, neither of which was related to any particular organism.