This exploratory study of ionospheric electron density Ne profile assimilation concerns the extraction of information on exospheric temperature Tex, atmospheric composition [O> and [N2>, meridional thermospheric winds, and solar EUV flux. These parameters are used as input variables to an ionospheric model and adjusted, one, two, or three at a time, to bring the model Ne profile into best agreement with an experimental Ne profile. The important ambiguity/uniqueness issue in the multiple-variable fit, which has yet to be addressed in the literature, is discussed. We found the following: (1) In a single-variable fit, any variable tested may be adjusted successfully to improve the data-model fit, but the validity of the derived variable generally depends on the validity of the values chosen for the fixed parameters. (2) The best fit model profile from a single-variable fit sometimes shows clear differences from the measured profile, indicating that multiple-variable fitting is warranted. The multiple-variable fit often greatly reduces the model-data profile differences and improves the error bars on the derived parameters. (3) Multiple-variable fits often show large variable correlations, indicating that variable determination is often not unique. (4) The meridional wind often shows weak correlation with other variables, suggesting that the meridional wind and any other parameter can be reliably extracted, provided that the other atmospheric variables are known. (5) [N2> often shows strong correlation with other parameters (except with the wind). The EUV flux and [O> also show large correlation. (6) The Tex-[O> and Tex-EUV pairs show medium to high correlation. (7) The three-variable fits nearly always show large ambiguities in the derived parameters. ¿ 2001 American Geophysical Union