Fluoride is able to augment cancellous bone mass in vertebral osteoporosis but is responsible for osteoarticular side effects in which microfractures are thought to be involved. During healing of these microfractures, a callus is formed all around the cancellous fracture line. Our hypothesis is that in fluoride-treated osteoporotic patients, calluses are bone sites where fluoride is focally deposited at a high concentration, and this could induce a local defect of calcification with a poor healing of microfractures. Our aim was to validate this hypothesis on several calluses following microfractures in undecalcified iliac cancellous bone from six women with osteoporosis (four fluoride treated and two untreated). Histologically normal iliac cancellous bone tissue, taken from a subject having neither fluoride treatment nor microfracture, was also examined. Selected areas, including new woven bone (calluses) and old lamellar bone, were carbon-coated and analyzed using an electron microprobe. Fluoride K alpha and calcium K alpha radiations were detected with wavelength and energy-dispersive spectrometers, respectively. In old lamellar bone at a distance from microfractures, the fluoride level was similar in normal and untreated osteoporotic patients but was slightly increased in treated osteoporotic patients. In untreated osteoporotic patients, the fluoride level was slightly higher (about 1.2 times) at the site of microfractures (lamellar and woven bone) than in lamellar bone far from such fractures, but fluoride was homogeneously distributed in lamellar and woven bone.(ABSTRACT TRUNCATED AT 250 WORDS)