The feasibility of using a collimated252Cf neutron source to measure regional changes in skeletal calcium was tested becausein vivoregional activation of diseased bone should offer advantages over the more widely reported total‐body calcium measuring techniques. Regional activation allows examination of discrete regions where the greatest changes in calcium content occur. Additionally, a simpler radiation facility is required for regional studies. Using a 5.5‐μg252Cf source, thermal neutron flux and absorbed dose were measured in a tissue‐equivalent phantom. Detection efficiency of49Ca γ rays for conditions simulating regional activation were measured using a 29‐cm‐diameter ×10‐cm‐thickness sodium iodide detector. Thesein vitromeasurements indicate that a collimated252Cf source can be used for regional neutron activation of the lower spine and legs. Preliminary calculations indicate that a 1–3‐mg source provides adequate count rates for statistical accuracy with a bone marrow dosage acceptable for human patients and normal subjects.