  We compare Far-UV, H-alpha, and optical broadband images of the nearby spiral
galaxy M33, to investigate the massive stars associated with the diffuse
ionized gas. The H-alpha/FUV ratio is higher in HII regions than in the DIG,
possibly indicating that an older population ionizes the DIG. The broad-band
colors support this conclusion. The HII region population is consistent with a
young burst, while the DIG colors resemble an older population with constant
star formation. Our results indicate that there may be enough massive field
stars to ionize the DIG, without the need for photon leakage from HII regions.
