An analysis of the mechanisms of elimination of o-125I-benzoate in the rabbit kidney on the basis of the inhibition of the secretionary transport by probenecid has shown that o-125I-benzoate is eliminated in the kidneys not only by glomerular filtration but by tubular secretion as well. An effect on the total amount of the drug excreted in the urine is exerted by tubular resorption (apparently by the process of passive diffusion), which exceeds tubular secretion. A comparison of the chromatograms of the plasma and urine before and after the competitive inhibition of the tubular active transport by probenecid revealed a higher share of o-125I-benzylglucuronide in the urine in the case of inhibition. The results suggested a partial share of the kidneys in total biotransformation of o-125I-benzoate. Excretion of the original drug and metabolites in the bile forms a negligible share (less than 1%) of total clearance in rabbits.