A non-destructive method based on instrumental neutron activation analysis (INAA) for the assay of aluminum in bone samples is described. The28Al signal obtained upon neutron irradiation includes contributions from both the reaction27Al(n,)28Al and31P(n,)28Al. The first reaction is with the thermal neutrons and the second one is with the fast neutrons. The contribution from the31P reaction is calculated from the fact that Ca/P ratio in bone mineral is constant and the amount of calcium can be measured from the thermal reaction48Ca(n, )49Ca. The aluminum values obtained by the INAA procedure agreed within 10% of those obtained by atomic absorption spectrophotometry. With this assay the levels of aluminum in normal bones (<70 g g–1 apatite) cannot be determined reliably but higher aluminum levles in bone biopsies associated with Al toxicity, e.g. some patients with renal osteodystrophy, can be determined with a precision of ±10%.