An IAEA biological RM IAEA-155 whey powder was analysed for phosphorus, as well as other 24 elements by INAA. The bremsstrahlung photons produced by ³²P is measured by a HpGe spectrometer. The interferences involved in P determination were comprehensively studied and this method was also applied to the determinations of P in several established biological NBS SRMs and proved to be reliable for a wide range of P contents in biological samples.