1. Microperfusion of tubules in situ was used to study the direct effect of sodium taurocholate on reabsorption of fluid by the proximal tubule of the rat.
2. Sodium taurocholate (0.1 mmol/l) in the tubular perfusate reduced proximal tubular fluid reabsorption by approximately 30%.
3. Thus, the proximal tubule appears to be a major site at which bile salts cause a natriuresis in the rat, and possibly in obstructive jaundice in man.