An acute load test was used to test the influence of dietary factors on urinary calcium excretion. In study 1, 10 fasting premenopausal women consumed test meals providing a moderate amount of protein (MP; 23 g), MP plus 23 mmol KHCO3 (MP+K), MP plus 23 mmol NaCl (MP+Na), and a high amount of protein (HP; 53 g), HP plus 70 mmol KHCO3 (HP+K), and HP plus 70 mmol NaCl (HP+Na). Protein was casein:lactalbumin (80:20), except for the treatments with added sodium chloride, to which only casein was added. In study 2, the effects of HP and HP plus 50 mmol KHCO3 (HP+K) were compared with those of MP or MP plus 7.5 mmol phosphate (MP+Pi), equaling the additional phosphate of HP, in 10 adult men. Subjects completed all treatments in random order. In study 1, the peak of calcium excretion was at 3 h for all treatments, except for HP+K, which indicated an acute hypocalciuric effect of potassium. Unexpectedly, there was no hypercalciuric effect of adding sodium chloride, nor was urine sodium increased. In study 2, calcium excretion was significantly higher with HP than with MP+Pi but not with MP at 3 h, indicating an acute hypercalciuric effect of protein alone. A hypocalciuric effect of potassium (HP+K compared with HP) but not of phosphate (MP compared with MP+Pi) was seen. An acute load test measuring changes 3 h postload was appropriate for examining the calciuric effects of protein and potassium bicarbonate, but not those of sodium chloride or phosphate in adults.