448 patients with chronic pyelonephritis were treated over periods ranging from a minimum of 5 to a maximum of 15 years with our special form of intermittent long-term therapy with chemoprophylaxis in the intervals, the antibiotics - mostly in the form of combinations - and chemotherapeutics in the treatment-phases were always used only on the base of several antibiograms. During the last 11 years synergistic bactericidic combinations of antibiotics were used to an increasing degree. 2. A comparison of the efficacy of our form of therapy used now (since 1965/1966) with the results already published: 1966 (therapy span 1960-1965), 1970 (therapy span 1960-1969), and 1972 (therapy span 1960-1971) showed the following quotes of a transmission into a standstill (questionable healing) of the disease: 1966 (without periodic change of the urinary pH) 36,1% 1966 (with periodic change of the urinary pH) 69,4% 1970 (synergistic combinations of antibiotics) 68,3% 1972 (synergistic combinations of antibiotics) 78,7% 1976 (synergistic combinations of antibiotics) 82,1%. 3. On the basis of our results we consider the combinations of synergistic bactericidic antibiotics as a real enrichment of the therapy of chronic pyelonephritis.