A study of 28 patients receiving a standard regimen of total intravenous nutrition (I.V.N.) for periods of > 14 days has shown the transient development of hypercalciuria in 14 patients (50%). The peak incidence of hypercalciuria occurred in 11 patients (39%) after 1 week of I.V.N. and hypercalciuria persisted for 1-4 weeks. In only one patient was hypercalciuria present at the end of the treatment period. Urine calcium (Ca) and nitrogen (N) excretion rates correlated significantly (r = 0.48 p < 0.001) and urine N excretion varied from week to week in parallel with urine Ca excretion in the hypercalciuric group of patients. There was no significant difference in urine Ca excretion between 12 patients who received 3.75 mmol Ca/day and 16 patients who received 8.75 mmol Ca/day. It is concluded that transient hypercalciuria may be related to increased protein catabolism and N excretion and that it probably does not indicate a major problem in mineral metabolism.