Cross-sectional studies have suggested that asthmatic patients receiving high dose inhaled corticosteroids and intermittent courses of oral corticosteroids have reduced bone mass. This prospective 2-yr study was undertaken to evaluate changes in bone density of patients receiving high doses of inhaled corticosteroids. Patients (n=33) (males aged 18-50 yrs, females aged 18-40 yrs) on inhaled corticosteroids 1,000-2,000 μg·day-1, were randomized in a double-blind fashion to either fluticasone propionate (FP) 1,000 μg·day-1 or beclomethasone dipropionate (BDP) 2,000 μg·day- 1. In parallel, three open control groups of the same age range were studied: asthmatics (n=8) receiving low dose inhaled corticosteroids (≤400 μg·day-1) (group A); chronic, severe asthmatics (n=8) receiving oral corticosteroids (≥10 mg·day-1) (group B); and healthy untreated volunteers (n=7) (group C). Bone densitometry scans (quantitative computed tomography (QCT) of spine; dual X-ray absorptiometry of spine, femoral neck, and single photon absorptiometry of forearm) were performed at baseline and after 6, 12 and 24 months of treatment. Biochemical bone marker measurements (serum osteocalcin, bone alkaline phosphatase, pro-collagen type 1 carboxy terminal propeptide, deoxypyridinoline and C-telopeptide of type 1 collagen) were collected every 3 months. Fifteen FP (mean age 36 yrs, six male) and 9 BDP patients (mean age 33 yrs, five male); completed the study. At 0 months, mean bone mineral density (BMD) was lower in patients receiving inhaled corticosteroids (both low dose and high dose) than in normal volunteers. In the FP-treated group, mean vertebral trabecular BMD quantitative computed tomography remained stable with no evidence of decline, whereas there was some decline in the BDP-treated group. The treatment difference between FP and BDP was statistically significant in favour of FP for quantitative computed tomography measurements after 12 months (p=0.006) and 24 months (p= 0.004). This study suggests that over 24 months, changes in bone density are minimal in patients on high-dose inhaled corticosteroids.