Voyager 2 ultraviolet spectrometer (UVS) solar occultation lightcurves at wavelengths 125--138 nm acquired during the Neptune encounter are compared with one-dimensional methane photochemical-transport models. Photoabsorption by methane (the photochemical parent) is expected to be the major source of opacity at these wavelengths, in which case the UVS lightcurves can be used to infer the strength of eddy mixing at altitudes above the methane photolysis peak and compatible CH4 mixing ratios in the lower stratosphere. For the p-T models adopted in this study, acceptable fits to the UVS lightcurves are obtained with eddy mixing coefficient values (K1/2) near the half-light altitudes (placed 550--600 km above the respective 1 bar levels) of 2--15¿106 cm2 s-1 (ingress) and 4--35¿106 cm2 s-1 (egress) and lower stratospheric (p>1.0 mbar) methane mixing ratio values (fT(CH4)) of 5--100¿10-5 (ingress and egress). The ranges in fT(CH4) and K1/2 reflect uncertainties in the background p-T structure and the application of different criteria for deciding what constitutes a ''good fit.'' For the nominal p-T models and a criterion based on replicating the spacing in altitude of the 125--138 nm UVS lightcurves, K1/2 values (near 0.2 μbar) of 107 cm2 s-1 (ingress) and 1--2¿107 cm2 s-1 (egress) and fT(CH4) values of ~1¿10-4 (ingress and egress) are indicated, with the egress results being more uncertain. These results are insensitive to photochemical details of the models. ¿ American Geophysical Union 1992