Iron Out - yellowing can happen because of minerals/metals in the water and Iron Out removes them from the fabric.

Rit White-Wash (found with Rit dye in the laundry section - safe for all fabrics that can be washed in hot water).

Blueing - is just an optical illusion and doesn't remove the yellowing, just covers it with blue which will appear to be "white" for a few washes.

-Grainlady

cascade powder and clorox 2 mixed together in a bucket of warm water to disolve and soak in, then tossed int he wash should do it...

years ago, when nurses wore 'whites' this was the 'trick' for them....