SummaryTwenty patients (males) with pulmonary surinfection on bronchitis or silicosis are included in this Prospective and controlled trial. Ten patients paired for age, weight and serum creatinine receive either Gentamicin or Tobramycin at similar maintenance dosage during ten consecutive days. The increase of serum creatinine after ten days of treatment is respectively of 12.4±6.2μmole/1 (SD) Under Tobramycin and 44.2±37.1βmole/I Under Gentamicin (p<0.05). Urinary excretion of two tubular enzymes: N-acetyl-β-D-glucosaminidase and Alanine Amino Peptidase increases significantly and correlatedly (py a proximal tubular cell dysfunction.