The Voyager 2 Ultraviolet Spectrometer measured the emission intensity of the He resonance line at 584 ¿ to be 0.34+0.2-0.15 R on the day side of Neptune. Our calculations of the He 584 ¿ intensity at Neptune using a partial frequency redistribution and inhomogeneous atmsopheric models show that the product of the volume mixing ratio (mole fraction), fHe, and the eddy diffusion coefficient at the homopause, Kh, is fHeKh=107 cm2 s-1 with upper and lower bounds to the uncertainty of about a factor of 3 and 9, respectively. If fHe is taken as the current Infrared Interferometer Spectrometer working value, fHe=0.19, then Kh==5¿107 cm2 s-1 with a similar uncertainty. This range of K overlaps that obtained from analysis of the hydrocarbon distributions on Neptune (Broadfoot et al., 1969). ¿The American Geophysical Union 1990