Twenty children and five adults with osteogenesis imperfecta were studied for one year or more, and thirteen of the patients were treated with sodium fluoride (0.25 to 0.90 milligrams fluoride per kilogram of body weight per day). No significant abnormality of calcium, phosphorus, nitrogen, magnesium, or potassium balance, serum chemistries, urinary amino acid excretion, or calcium dynamics was detected before treatment, nor were changes seen during treatment. The over-all results do not warrant the general use of fluoride for the treatment of osteogenesis imperfecta but do warrant further study, especially of the dose-related effect.