We have calculated the steady-state distribution of secondary electrons in dense interstellar clouds that are produced in collisions between primary cosmic rays and thermal gas atoms. We find that if the magnetic field in such clouds is approx.100 microgauss, then the synchrotron volume emissivity in the clouds is sufficiently large that discrete, isolated clouds may be identifiable in the Galactic radio background: if the field is as large as 1 milligauss, the synchrotron radiation from nearby clouds would be the dominant feature of radio maps of the Galaxy. Energetic secondary electrons in dark clouds will also manifest themselves through bremsstrahlung and inverse Compton contributions to the ..gamma..-ray background and by increasing the hydrogen ionization rate in the clouds: calculations of the magnitude of these effects are given.