1. A review of the literature on the normal variations in bone mass in a given population in relation to age, sex, nutritional and genetic background shows several lacunae in our knowledge. Consequently, the separation of milder degrees of osteoporosis is difficult and the definition of osteoporosis itself is uncertain.

2. This paper presents a necropsy study to determine variations in the bone mass that occur with age and sex in a normal Indian population in the Delhi area. Two hundred persons between nine months and seventy-six years of age who died by accident and with no evidence of chronic disease were studied.

3. The parameters of bone mass employed were : apparent bone density, ash per millilitre of bone, cortical thickness and visual grading of porosity of bone in macerated specimens. The first lumbar vertebra, the iliac crest, the fourth rib and the femoral shaft were the bones evaluated.

4. After an initial rise up to the third decade, the apparent bone density and ash per millilitre showed a progressive and significant decline with age in all the three trabecular bones: vertebra, iliac crest and rib. Although these values were in general lower in the females than in males at all ages, and the rate of decrease with age was faster in them than in males, it was only in the rib that a statistically significant difference between the sexes could be established with respect to decrease with age.

5. Decreases in apparent bone density and ash per millilitre of the vertebral bone with age were associated with an increase with age in the porosity as assessed by visual grading.

6. In the case of the femur no significant change was demonstrable with age in any of the parameters used in the present study.

7. From a comparison of the values for apparent density and ash per millilitre with grading of macerates and histological preparations, it is suggested that osteoporosis may be said to be present in this population if the apparent bone density is less than 020 and 046 in the vertebra and the iliac crest respectively or ifthe ash per millilitre is less than 0l2 in the vertebra.

8. The study has revealed that 44 per cent of persons studied in this sample over the age of fifty exhibit significant osteoporosis. It is considered possible that nutritional factors such as protein-calorie malnutrition may be responsible for this relatively high incidence.