Whole animal clearance studies and in vitro microperfusion studies were performed to examine the effect of atrial natriuretic factor (ANF) on the rabbit proximal tubule. Infusion of ANF into rabbits resulted in an increase in glomerular filtration rate and a natriuresis and diuresis. To determine whether ANF has a direct proximal tubule effect to account for part of the observed natriuresis, proximal convoluted tubules (PCT) and proximal straight tubules (PST) were perfused in vitro. Addition of 10(-9) M ANF, a concentration recently measured in vivo during volume expansion, to the bathing solution of PCT caused no significant change in volume absorption. Addition of a pharmacological concentration of ANF (10(-7) M) to either the bathing solution or the luminal perfusate of PCT resulted in no change in volume absorption. When added to the bathing solution of PST, 10(-7) M ANF did not have an effect on volume absorption. ANF did not affect the transepithelial potential difference in any protocol. In conclusion, these data show that ANF does not affect transport directly in the proximal tubule.