IUE spectra of Jupiter are examined in light of recent models put forward to explain the anomalously bright ultraviolet emissions seen from the upper atmospheres of the outer planets. Chi-squared fits of the IUE spectra with model spectra produced by two proposed excitation mechanisms, electron impact and fluorescence of solar radiation, result in consistently higher &khgr;2 values for the solar fluorescence model. We find no conclusive evidence in the IUE data for the dominance of solar fluorescence over electron excitation in producing the Jovian dayglow emission. ¿ American Geophysical Union 1989