Twenty-one healthy volunteers and 281 patients were given an oral dose of 3 g creatinine. The creatinine concentration in serum was determined before and 24 hours after loading. Creatinine concentration in 100 ml serum rose, on average, 0.05 mg in healthy subjects, 0.1 mg in patients with renal disease with a creatinine concentration of less than 1.1 mg per 100 ml serum, 0.2 mg with creatinine concentrations of 1.1–1.2 mg per 100 ml serum, 0.4 mg with creatinine concentrations of 1.3–1.4 mg per 100 ml serum and more (0.5–5.0 mg) with a serum creatinine concentration higher than 1.4 mg per 100 ml serum before loading. There was no difference between men and women with normal creatinine concentrations. On 213 occasions, 19 out of 202 patients with a normal creatinine concentration had a rise of at least 0.4 mg per 100 ml serum. On 38 occasions, 8 out of 35 patients with creatinine concentrations of 1.3–1.7 mg per 100 ml serum before loading had a maximum rise of 0.2 mg per 100 ml serum.Creatinine loading ca...