We carried out a pilot project to examine the alterations in trabecular bone remodeling activity of spayed Beagle dams exposed to 0.7 mg/kg body wt/day of sodium fluoride (NaF) for a 6 month period. The results indicated that short-term NaF administration does activate trabecular bone remodeling activity by stimulating the formation of new Basic Multicellular Units (BMUs) of bone remodeling activity. However, interference with bone cell differentiation, with the functional efficiency and/or life-span of individual osteoclasts and osteoblasts followed. Cellular toxic effects appear early with NaF administration, and as such, suggest that the increases in bone mass seen early in the course of NaF treatment may be negated by prolonged administration of this substance. However, preservation of bone mass will probably result with long-term therapy, due to decreases in numbers of bone cells, in their functional efficiencies, and in their individual life-spans.