The study was designed to determine the calciuretic effect of furosemide and its impact upon calcium balance during chronic (25 days) furosemide administration to growing rats. Experiments were performed on 18 six-wk-old rats. Nine animals received furosemide, and 9 served as controls. The administration of furosemide in a dose of 40 mg resulted in a significant increase in calcium excretion in the treated group; urinary calcium excretion almost doubled that of the controls during the first 24-hr collection (3.74 +/- 0.44 mg in the treated animals compared with 1.90 +/- 0.15 mg in the controls; P less than 0.05). The average daily urinary calcium excretion during each of four subsequent 6-day periods remained approximately three-fold higher in animals which received furosemide compared with controls (P less than 0.001 for each 6-day period). The furosemide-induced increase in urinary calcium excretion did not diminish with time. Sodium excretion did not significantly increase either acutely or chronically in response to furosemide. Daily urinary volume increased approximately 40 to 60% in the furosemide-treated group compared with that of the controls (P less than 0.001). The cumulative calcium balance in the control group exceeded by 7% that of the furosemide-treated animals [2696.3 +/- 20.8 mg versus 2518.6 +/- 20.1 mg (P less than .001]. The findings indicate that distal nephron compensatory mechanisms effecting sodium conservation following furosemide do not result in similar conservation of calcium. Calcium balance may be deleteriously affected.