A procedure for the determination of 2 '°Pb is presented, which is based upon the /?-spectrometric assay (utilizing a liquid-scintillation counter) of 2,ü Bi in radioactive equilibrium. Separation of 210 Bi from the sample matrix as well as from other /^-emitters is achieved quickly, simply and selectively using a purge and trap technique based upon the generation and subsequent absorption of BiH 3 on a prepared filter paper. Advantages of this method include: 1) radioactive equilibrium between 2,0 Pb and 210 Bi is relatively quickly attained; 2) the external background signal in liquid-scintillation counting is very low; 3) no quenching corrections are necessary, as the sample matrix is invariant; and 4) because of the high counting efficiency, only short measuring times are required.