The long bones of mammals are altered detrimentally in response to spaceflight and disuse. These alterations are characterized by reduced bone mass (osteopenia) and reduced mechanical strength. Experimental disuse osteoporosis models have been developed to mimic the unloading aspects of spaceflight. The suspension model for osteoporosis has been utilized in rats, whereas the present investigations utilize mice. The effects of suspension were show n to be dependent on the age and the sex of the mice, and the general mechanism for the decreased mineral and collagen content of the bones from suspended mice was seen to be growth suppression. This suppression was comparable to that observed in mice undergoing dietary caloric restriction. To determine the effects of this suppression on the characteristics of the mouse long bones, the bone was defined in terms of its mechanical and material characteristics. Upon the establishment of the suspension model in mice, a number of treatments for osteopenic effects were superposed. Oral calcium, fluoride and etidronate supplements were utilized as treatments. Both localized and whole-body electromagnetic fields were implemented, as well. These studies suggest that the use of calcium supplements largely prevents the osteopenic effects of suspension in mouse long bones, and that a variety of electromagnetic fields may be useful in promoting osteogenesis. The localized fields were generally more effective when applied at an orientation lateral to the length of the bone than when applied axial to the bone. One whole-body field was observed to have detrimental effects on bone mass and mechanical parameters, suggesting deleterious effects of the fields eith er local to the bones or systemic in nature. A series of in vitro experimdents in dicated that the effects of suspension and whole-body fields, at the cellular level, are lost upon nonsuspension or removal of the field. The results indicate th at mouse suspension is an appropriate model for osteopenia, and that calcium and certain electromagnetic fields may largely prevent the osteopenic effects.