In an open study of 49 episodes of intra-abdominal sepsis in 48 patients, metronidazole was used in combination with tobramycin, and each was given by intravenous infusion. All patients were also treated by appropriate surgical operation. The ages of the patients ranged from 21 to 89 years, and both sexes were equally represented. Twenty-two patients had abscesses drained. Thirty-eight of 49 treatment courses gave good results. Eight patients recovered, although slowly, and three were classified as failures. Of the failures, one instance was attributed to infection with Staphylococcus aureus, and recovery was satisfactory when cloxacillin sodium was given. The other two failures were due, in part, to shock caused by trauma and blood loss in one instance and disseminated anaplastic lymphoma in the other. No significant adverse effects were attributable to the antibiotics.