A fast, accurate, and stable three-dimensional interpolation algorithm of central type is proposed to reconstruct the electromagnetic field in any point of a given volume external to an arbitrary source. It is based on a new sampling representation which allows us to drastically reduce the number of needed data when compared with conventional λ/2 sampling, thus significantly lowering measurement time and storage requirements when characterizing field distributions in electrically large domains. Moreover, for large sources it is also computationally convenient with respect to modal expansions or source integration methods. The efficiency and stability of the developed interpolation algorithm are assessed by means of numerical tests. ¿ 1999 American Geophysical Union <