The pharmacokinetics (PK) of an oral sulfate solution (OSS) for bowel cleansing preparation was studied. OSS (30 g of sulfate) was split between 2 doses, 12 hours apart. Safety measures included electrocardiography, vital signs, adverse events, hematology, blood chemistry, and urinalysis. Six adult patients with moderate renal disease (MRD), 6 with mild-moderate hepatic disease (M/MHD), and 6 normal healthy volunteers (NHVs) completed the study. Adverse events were mild to moderate in severity and were mainly limited to headache and expected gastrointestinal symptoms. Serum sulfate levels were highly variable at all times, even after adjusting for baseline. Sulfate was higher in MRD in comparison to the other groups. The C(max) and AUC were higher in the patients, but no statistically significant differences emerged. Sulfate levels returned to predose values within 54 hours after dosing. No electrolyte disturbances occurred. Urinary sulfate excretion was approximately 20% of the dose. OSS was well tolerated. The types and severity of adverse events were similar to those seen in large phase III trials. While patients with MRD had elevated sulfate, the levels were less than those in renal failure and did not alter biochemical parameters that are associated with hypersulfatemia.