6 mos. or 5,000 miles is the interval set by Lexus for service/oil change. If you live in areas of "extreme conditions" (non-specified) then it is recommended to do it sooner. Since the engine temperature is regulated by the cooling fan and the coolant, it really matters very little weather you live in Dallas or Butte, MT as far as how hot the oil gets, so forget letting some dealer service writer talk you into intervals less than 5,000 miles or 6 months. Now if you live at the end of some dirt road or have excessive dust or pollen in the areas in which you commonly drive a shorter interval might be justified. And by the way, the oil change intervals are soon to be increased to 10,000 miles on GS and IS as they already are on the current `10 RX350 & GX460. It's because Lexus has now begun to use synthetic oil.