Abstract We have used a one-dimensional methane photochemical model to analyze Voyager observations of hydrocarbons and hazes in the stratosphere of Neptune. Vayager IRIS spectra provide information about the global average C 2 H 2 and C 2 H 6 mixing ratios for p > 0.1 mbar. The UVS lightcurves provide constraints on CH 4 and C 2 H 4 in addition to C 2 H 2 and C 2 H 6 but only at the solar occultation latitudes and for lower pressures. The model-predicted hydrocarbons are very sensitive to the height profile of the eddy diffusion coefficient ( K ). For both data sets K varying inversely with the atmospheric number density to some power produced poor results. Good agreement with the data requires that K be weak in the lower stratosphere ( K ≃ 2 × 10 3 cm 2 sec -1 for p⪊2 mbar) but fairly vigorous in the upper stratosphere ( K > 5 × 10 7 cm 2 sec -1 for p⪉ 0.5 mbar), i.e., a rapidly mixed upper stratosphere overlying a stagnant lower stratosphere with a rapid transition in between. The model C 2 H 6 and C 2 H 2 mixing ratios are also sensitive to the reaction rate constants of C 2 H 4 + H and CH 3 + C 2 H 3 . Notably, we must use the present upper limit for the C 2 H 4 + H rate to best fit the model results to the observations. We are able to reproduce the IRIS C 2 H 2 and C 2 H 6 emission features well, less so the UVS occultation lightcurves. Since the transport of C 2 H 2 , C 2 H 6 , and other hydrocarbons produced from methane photolysis out of the stratosphere is by ice haze formation and sedimentation, we compared model haze predictions to PPS and IRIS observations. For solar maximum fluxes (Voyager encounter conditions) the model mass production rate is 1 × 10 -14 g cm 2 sec -1 . C 2 H 6 is the dominant haze component (75%), with the remainder coming from C 2 H 2 and C 3 and C 4 compounds. Balancing the above haze production rate by the sedimentation rate for 0.25-μm radius particles (upper limit to particle radius from PPS observations) yields a total haze column burden slightly above the PPS upper limit. However, lifetime analysis indicates that the model haze production rate should be averaged over solar minimum and maximum conditions. Under these conditions the model haze density is consistent with the PPS data. The predicted C 4 H 2 and C 2 H 6 haze column densities are consistent with the lack of ice signatures in the IRIS spectra.