Objectives: Little is known about the relationship between the renal and gastrointestinal excretion of potassium in humans. This information is important in light of strong associations of potassium intake with hypertension and occlusive stroke. Methods: We determined the relationship between fecal and urinary excretion of potassium under both fixed and variable potassium intakes using our unpublished archival data and published data of others. Twenty-five subjects were evaluated. Results: On a fixed, low oral potassium intake (61.2 ± 4.7 mmol/day; mean ± SD), there was an inverse relationship between fecal and urinary potassium excretion (r = −0.66, p = 0.040). In studies in which potassium intake varied between 61–135 mmol/day, fecal and urinary potassium excretions were positively correlated (r = 0.58, p = 0.024). Considerable within-and-between-subject variation was observed in the relationship between fecal and urinary potassium excretion. Conclusions: Inter-individual variation in fecal potassium excretion may arise from both variation in dietary potassium intake and intrinsic individual differences in the renal versus gastrointestinal handling of potassium.