Forty-two patients with a radiologically confirmed diagnosis of chronic pyelonephritis were treated with 1 g carindacillin every 6 hours over a period of 6 weeks. An underlying urological disease was present in 84% of the 38 patients for whom sufficient data were available for evaluation. The results of carindacillin treatment, as judged by bacteriological evaluation 1 month post-treatment, were good in 12 (32%) and moderate in 9 of the patients. This success rate was remarkable in that all of the patients had been treated previously with one or more other antibiotics and chemotherapeutic agents with little or no response. The authors recommend that, because carindacillin has proved so valuable in treating chronic as well as acute urinary tract infections, its use should be limited to patients with serious disease who have not responded to other treatment.