  Recursion formulae are derived for the calculation of two centre matrix
elements of a radial function in relativistic quantum mechanics. The recursions
are obtained between not necessarily diagonal radial eigensates using arbitrary
radial potentials and any radial functions. The only restriction is that the
potentials have to share a common minimum. Among other things, the relations so
obtained can help in evaluating relativistic corrections to transition
probabilities between atomic Rydberg states.
