Techniques were developed to measure small changes of calcium in the forearm and spine in vivo by neutron activation analysis using two sources of 252Cf in a hospital environment. Using purpose-built part-body counters and bilateral irradiation with 7.5 cm premoderation between the sources and the bone, peripheral bone was measured with a total source strength eventually as low as 50 mCi. Two methods of spectral analysis were used and compared. Patient studies of the forearm were successfully undertaken, with a precision of 2.6% which included patient movement, and an annual bone dose of less than 10 rem and skin dose of 35 rem from six measurements. Two 100 mCi sources were used for measurements of the lumbar spine. Care was taken to minimise the problems of non-uniformity of activation which are present using unilateral irradiation. Emphasis was placed on measuring the bodies of the vertebrae with adequate sensitivity and uniformity, and the spinous processes and arches with low sensitivity. A whole body counter was used for the bilateral detection of the induced activity. The precision of the method was 3.0% with an annual peak bone dose of 2.1 rem and skin dose of 18 rem from three measurements.