Dual-energy x-ray absorptiometry (DEXA) is now an established method of measuring bone mineral density (BMD) in humans. We have applied the technique to measuring BMD in the rat. The short-term precision of the technique was assessed by calculating the BMD coefficient of variation at the rat spine (1.20%), total femur (0.52%), proximal femur (1.16%), midfemur (1.00%), distal femur (0.96%), and proximal tibia (2.2%). The long-term precision of femoral measurements in rat cadavers over a 4 week period was 0.72% for the total femur and 1.2% for the distal femur. The accuracy of the technique was assessed by comparing DEXA-measured bone mineral content (BMC) in vitro and in vivo with ashed BMC. Results indicated a highly significant positive correlation between in vitro DEXA measurements and ash BMC (r = 0.99) and between in vivo DEXA measurements and ash BMC (r = 0.89). The ability of the technique to detect bone loss was assessed at the femoral site by comparing the BMD of ovariectomized (OVX) and sham-operated rats at baseline and at a 1 month follow-up. There was no significant difference in BMD between the groups at baseline. However, at 1 month follow-up the OVX group showed a significant (p < 0.001) decline in BMD at the distal femur (-8.6%) and in the total femur (-4.8%) compared with sham-operated rats. A comparison of retired breeder female rats with age-matched nulliparous rats indicated that the BMD of retired breeder rats was significantly lower than that of virgin females at all femoral sites (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)