That different mechanisms are involved in the secretory processes by the liver and the kidney of various dyes has been indicated by Sporter (1959), Kim and Hong (1963). Andrews (1958). suggested that a striking difference in the dye-secretory mechanism existed even in the same organ from species to species. Hence, the attempt has been made to study in the rabbit the secretory processes by the live. and the kidney of either phenol red (PSP), bromsulfalein (BSP) or green in the presence of Na-acetate, Na-taurocholate, P-Aminohippurate (PAH) or Benemid. In 37 rabbits, weighing about 2kg., anesthetized with ether, a dye was administered in such 8 manner that the plasma concentration was kept at a relatively constant level throughout the whole experimental period. Hepatic bile sad urine samples were quantitatively collected through the canulae which were previously inserted into the common bile duct (with the cystic duct ligated) and the urinary bladder, respectively, while arterial samples were taken from a femoral artery. After 50 min from the onset of dye administration, these samples were obtained every 10 mit for a period of 40 min. This was followed by the administration of either Na-acetate, Na-tauro-cholate, PAH or Benemid with a repetition of the same sample collecting procedures just stated. The results may be summarized as follows: 1) Na¡¤acetate augmented urinary clearance of PSP by nearly 300 per cent, but lowered urinary BSP clearance by about 50 per cent. It enhanced biliary BSP clearance by 40% and had no effect on biliary psp clearance. 2) Na-taurocholate lowered biliary and urinary clearance of PSP by 10 per cent and 30 per cent respectively, and had no effect on both biliary and urinary clearance of BSP. 3) PAH lowered both biliary and urinary excretion of BSP and PSP, while it lowered the biliary excretion of indocyanine green which was excreted only in the bile. 4) Benemid suppressed BSP excretion by the liver and the kidney. 5) raper chromatographic analysis of PSP and of BSP in the bile and urine samples gave the following results: a) PSP Ivas excreted in the urine and bile only in free forms, and no modification in the excretory pattern was brought about by Na-taurocholate. b) BSP was excreted in the urine in 4 different conjugated froms and in the bile in both 3 different conjugated forms and in a free form. Na-taurocholate modified the excretory pattern of the urinary BSP.