PROTOCOL OUTLINE: This is a randomized, double blind study. Patients will be stratified according to sex (male vs female) and osteoporosis disease severity (mild vs severe). Patients are randomized to one of two treatment arms.

Patients undergo bioavailability assessment to confirm the ability to absorb alendronate.

Arm I: Patients receive calcium and vitamin D supplements with a placebo daily for one month.

Arm II: Patients receive calcium and vitamin D supplements with oral alendronate daily for one month.

Treatment continues if differences are seen in bone mineral density between the treatment arms.

Patients are followed for biochemical response at week 6, 12, and 52. Bone mineral density is measured at 1 year and 2 years.

PROTOCOL ENTRY CRITERIA:

--Disease Characteristics--

• Diagnosis of cystic fibrosis Mild to moderate lung disease
• At least one site specific (spine or femur) bone mineral density representing low bone mass or osteopenia (greater than 1 standard deviation below peak bone mass)

--Prior/Concurrent Therapy--

• Endocrine therapy: At least 3 months since prior corticosteroids

--Patient Characteristics--

• Performance status: Ambulatory
• Renal: Creatinine no greater than 3 mg/dL No renal failure
• Other: No history of esophagitis No allergies to alendronate Not pregnant Fertile female patients must use effective barrier contraception or progestin only oral contraceptives (e.g., norethindrone) Ability to comply with treatment No intestinal problems other than cystic fibrosis