Treatment for acute interstitial nephritis (AIN) was examined in a retrospective study of 27 cases of AIN confirmed by kidney biopsy, and the results were statistically evaluated. The clinically determined serum creatinine values were taken as the criterion. The observation period ranged from 9 months to 2 1/2 years. The prognosis for seven patients who had received steroid preparations in addition to antibiotic and diuretic drugs in the early phases of the disease was significantly better than that of the other 20 patients who had been treated with only antibiotics and diuretics (p less than 0.05). Since the grade of severity of AIN in the two groups was almost identical (determined by maximal serum creatinine values) the two groups could be compared statistically.