Auto ISO functions correctly in every mode except Program. Program mode is probably the setting where I would apply this option most often. I have Thom Hogan's D2x guide and he mentions that it only works in program when 30 seconds is reached as a shutter speed. Well, I worked it past said 30 seconds in Program mode and the ISO always stays on my operator setting of 100 ISO. All other modes have no problem with applying the Auto ISO liberally. In fact I tested this setting on my D70s and found functioning perfect in every mode under many different conditions. Out of frustration I set the D70s next to the D2x for a little happy karma. No dice. Any adivce is greatly appreciated.