Sisomicin is an aminoglycoside effective against gramnegative germs. The sensitiveness of coli, proteus, pseudomonas and klebsiella ranges from 0,1 to 0,4 mcg/ml. Germs with inhibition-values of up to 1 mcg/ml are certainly Sisomicin-sensitive. The side-effects of Sisomicin resemble those of other aminoglycosides, as for instance lesions of the VIIth cranial nerve and the kidney. Since aminoglycosides have a relatively small therapeutic range between toxicity and effective minimal-concentration, investigations are important especially in children. 66 children of different age groups received Sisomicin in doses of 3 mg/kg, 2 mg/kg and 1 mg/kg, and examined pharmacokineticly. Serum-levels were measured after 30 min 1, 2, and 4h, in some cases also after 6 and 8 h. In a separate group we determined the values after 5, 10, 15, 20, 30 and 40 min. The urinary output was controlled and the content of Sisomicin in meconium determined. Based on these results we recommend an individual, Sisomicin dosage for each age group. Clinically the Sisomicin proved to be well tolerated and effective antibioticum.