The effect of furosemide on gentamicin excretion and tissue accumulation was studied with clearance techniques in anesthetized rats, at two different infusion rates of saline or Ringer solution. Gentamicin (-20 ). An infusion of the same solution at 1.2 ml/h immediately followed and was continued for 3 h. Collection of blood and urine samples began 1 h after priming dose and consisted of four consecutive clearance periods of 30 min each. At the end of each experiment, the kidneys were excised and divided into cortex and medulla for tiasue analysis of gentamicin.(ii) High fluid infusion rate. Saline (four rats) orRinger solution (two rats), at a rate of 6.3 ml/h, was infused for 1 h preceding the administration of inulin and gentamicin as described in (i) and continued for 3 h thereafter.(iii) Low fluid infusion rate plus furosemide.A 4-h infusion of Ringer solution, 1.2 ml/h, containing furosemide (priming dose, 5 mg/kg; sustaining dose, 5 mg/kg per h), was started 1 h before the administration of inulin as in (i) in each of six rats with and without gentamicin.(iv) High fluid infusion rate plus furosemide.