For condensed systema beta radiation is exponentially absorbed with an absorption coefficient, mu , given by: mu = (1 + M/100)/1.27 x 55E/sup 3/2/, where mu is given in units of cm/sup 2//mg, E is the maximum energy of the beta spectrum in millions of electron voits, and M is the average atomic weight of the absorbing medium. This relation is applied to radiation-dose calculations for strontium-90 in equilibrium with its daughter, yttrium-90, deposited in bone. (C.H.)