Renin secretion has been hypothesized to be inversely related to the tubular sodium concentration or load. Using rat kidney cortex slices, in vitro renin secretion was measured as a function of sodium concentration of the medium. We found, as have many others, that renin secretion increases with increasing medium sodium concentration. However, in the presence of 10<sup>-3</sup>m ouabain, renin secretion decreased with increasing medium sodium concentration. We also found that intracellular sodium concentration varied directly with medium sodium both in the presence and absence of ouabain. Furosemide, a known renin stimulator in vivo, had no effect on renin secretion from tissue slices. Although obvious differences exist between in vitro and in vivo results, no simple relationship may exist between intracellular sodium concentration and renin secretion.