  The issue of retarded long-range resonant interactions between two molecules
with oscillating dipole moments is reinvestigated within the framework of
classical electrodynamics. By taking advantage of a theorem in complex
analysis, we present a simple method to calculate the frequencies of the normal
modes, which are then used to estimate the interaction potential. The main
results thus found are in perfect agreement with several results obtained from
quantum computations. Moreover, when applied in a biophysical context, our
findings shed new light on Frohlich's theory of selective long-range
interactions between biomolecules. In particular, at variance with a
long-standing belief, we show that sizable resonant long-range interactions may
exist only if the interacting system is out of thermal equilibrium.
