Within the framework of a prospective study, 71 children of various age groups were treated with amoxycillin, a new semi-synthetic broad-spectrum penicillin. Of this number, there were 64 cases of pyelonephritis, 6 of respiratory infections (one combined with salmonellosis) and one case treated prophylactically. The average duration of treatment was 14 days, and the dosage 100 mg/kg body weight. The cases of pyelonephritis were treated strictly in accordance with sensitivity studies – in general, the bacterial isolates were very sensitive to amoxycillin. In 5 of the respiratory cases, there was a clinically proven therapeutic success. 63 of the 64 cases of pyelonephritis were fully followed-up. In 45 cases (71.4%), there was complete sterilisation of the urine, in 18 cases (28.6%), complete sterilisation was not possible, but only in one case, there was persistence of a sensitive organism. In 17 cases, either a development of resistance or a change of pathogen was observed. In cases of the appropriate diagnosis, amoxycillin showed itself to be adequate for the treatment of bacterial infections and, in particular, for the initial treatment of pyelonephritis. It also showed itself to be exceptionally well tolerated with minimal gastrointestinal side-effects – due note must be taken, however, of macropapular exanthema.