In terms of the Bessel functions, we characterize smooth solutions of some convolution equations in the complex plane and prove a two-radius theorem for solutions of homogeneous linear elliptic equations with constant coefficients whose left-hand sides are representable in the form of a product of some non-negative integer powers of the complex differentiation operators d and d. Keywords. Convolution equation, mean-value theorem, Bessel function, distribution, spherical transformation., Introduction The convolution equations generated by distributions with compact supports and the corresponding mean-value theorems were investigated by many authors (see, e.q., [1,2]). In particular, Volchkov [2, Part 3, Chapter [...]