We present a study of the variable X-ray source populations in the Antennae galaxies and a small sample of nearby star-forming galaxies. We find that source variability does not affect the shape of their X-ray luminosity functions. Several of the sources detected in the Antennae exhibit a wide range of spectral variability patterns. Finally, from our study of a small sample of nearby star-forming galaxies, we find a weak indication for variations of the shape of their luminosity functions.