The intrinsic (material) quality of cancellous and cortical bone was evaluated in vivo from the measurement of reflection ultrasound velocities in the ulna. In cancellous bone, the reflection ultrasound velocity was inversely correlated with age in normal women (r = -0.48, p = 0.001), with a significantly lower mean value in 32 normal postmenopausal women than in 14 premenopausal women (3124 versus 3341 m/s, p < 0.0001). In 32 untreated osteoporotic women the cancellous bone velocity was lower than in normal postmenopausal subjects (2906 versus 3124 m/s, p = 0.0001). Following treatment with slow-release sodium fluoride plus calcium citrate (mean 2.4 years in 33 osteoporotic patients with no fracture during treatment), the cancellous bone velocity was significantly higher than in untreated osteoporotic women (3082 versus 2906 m/s, p = 0.0002) and was not significantly different from that in normal postmenopausal women. The cortical bone velocity displayed similar trends, but the changes did not attain statistical significance. The measurements were repeated approximately 9 months later in 9 untreated and in 20 treated patients; in 5 additional patients, the measurements were made both before and after 9 months of treatment with slow-release sodium fluoride and calcium citrate. The cancellous bone velocity increased significantly (p = 0.046) in these patients, from 3008 m/s before treatment to 3112 m/s after the first 9 months of treatment. The velocity rose significantly from 3037 to 3167 m/s (p = 0.017) in patients treated for a short time (12-30 months at first measurement), but it did not change in untreated patients or those treated for more than 30 months. Thus, the material quality of cancellous bone decreases with normal aging and is reduced further with the osteoporotic process. This impaired quality may be corrected by treatment with slow-release sodium fluoride plus calcium citrate.