Bone mineral density (BMD) of lumbar vertebral bodies in the lateral projection were evaluated using dual-energy X-ray absorptiometry (DEXA) with respect to reproducibility of spinal bone measurements in two projections in healthy men, age-related bone mass changes in healthy women, and the bone mass in osteoporotic women. The BMD of the third lumbar vertebral body in the lateral projection (L3-LAT-BMD) and of the entire third lumbar vertebra in the anteroposterior projection (L3-AP-BMD) were measured with DEXA. The BMD of the distal metaphysis and distal diaphysis of the left radius were measured by single photon absorptiometry. The coefficient of variation in six men aged from 24 to 28 years was 1.7% for L3-LAT-BMD and 1.8% for L3-AP-BMD. In 82 healthy women ranging from 26 to 69 years of age (mean 50 years), BMD decreased rapidly after 50 years of age and above at all measured sites. However L3-LAT-BMD value showed wide distribution and decreased at an earlier age. Correlations within the two BMD values in the same bones were high (r = 0.799 for the vertebra and 0.803 for the radius), while those for any two BMD parameters for different bones were relatively low, with r values varying from 0.456 to 0.560. In 22 women with involutional osteoporosis ranging from 54 to 75 years of age (mean 65), values for L3-LAT-BMD and BMD of the distal metaphysis of the radius were lower than values predicted based on BMD of healthy women.(ABSTRACT TRUNCATED AT 250 WORDS)