This is an overview of to take out the cabin air filter for 1993&1994 LS400, I don’t know if 1990-1992 have cabin air filters.
http://us.lexusownersclub.com/gallery/show..._Removal?full=1

At first all the wires looked intimidating with the panel off; one of the wing nuts is circled:
http://us.lexusownersclub.com/gallery/show...de_of_the_panel

The cover looks like this with the two wings nuts at the end (I recommend you cover the carpet and mats beneath with some plastic or old cloth because leaves and dirt is going to spill out as soon as you take out the cover)
Pull the first filter out 75% of the way and then tilt it slightly to the left and then take it out. Pull the second on toward your self and do the same:
http://us.lexusownersclub.com/gallery/shows/The_cover

Mine looked like these:
http://us.lexusownersclub.com/gallery/shows/Air_Filters

Do you have a picture of a new filter next to the old one? Are the new one's white?
JimA

Agreed... lets see the new ones !!!

Samething not white:

If anyone wants a pic of some REAAAAALY dirty ones I can say the ones that came out of my 93 last changed who knows, are filty.

Is this process similar for a '97?

Forget it. I just figured it out and it was REALLY easy. In the '97 (and other applicable) LS400s, you just need to open the glove box and remove that little insert in the back, giving you access. Then there is a white panel with two little clips on it that can be carefully pried off with a flathead screwdriver. The cabin air filter is in sight!!!! Remove it and replace everything!