Polly: Undenatured whey is whey that has not been heated enough to ruin its healing properties. Heating destroys the immunoglobulins and breaks the peptides. Undenatured whey contains glutyl-cysteine (a peptide) rather than just cysteine.  Glutyl-cysteine and cystine are what the cells need to make glutathione. Undenatured whey will raise glutathione levels. This whey will also help resolve anemia. Those with AIDS and CFIDS have found it invaluable.
However, there are some drawbacks to whey. Because of the high cysteine and cystine content, there is considerable debate over whether it is advisable for those who are mercury poisoned. Cysteine will move the mercury around. Too much cysteine will also suppress thyroid. Another problem with whey is that it contains a relatively high amount of tryptophan compared to milk or cheese. Too much tryptophan could be harmful.
Undenatured whey is essentially raw whey, but legally they have to call it pasteurized in order to sell it. They use microfiltering to make sure there is no bacteria in it. The method by which they do the microfiltering is different for each company. Therefore you will get some differences in effectiveness between the products.
The brand called Immunocal is excellent, but it is about twice the price of the other undenatured whey products. It is from a network marketing company, Immunotec, making it somewhat difficult to buy. You can’t just call up and order some. You need to have a sponsor or become part of their sales force, at least in name only. Phone: (888) 917-7779 or (450) 424-9992 and website: http://www.immunotec.com or http://www.immunocal.com. The Immunocal product is approved for Medicare—meaning that under some circumstances (like AIDS or severe chronic fatigue), your insurance might pay for it, assuming you send them the correct forms. The people at Immunocal, Inc, can help you get the forms you need.
IMUPlus is another undenatured whey product. It can be purchased through Allergy Research / Nutricology, phone (800) 782-4274 or or website http://www.nutricology.com. There is also ImmunePro undenatured whey. ImmunePro is available from N.E.E.D.S., phone (800) 634- 1380, website http://www.needs.com.
For those few who have access to raw milk, and who are not so immunocompromised that they worry about the bacteria and viruses in raw milk, they can make their own undenatured whey. Whey is the liquid left over after making cottage cheese. The bacteria have eaten the lactose (milk sugar), so there shouldn’t be much left in the whey. The whey will have very little casein in it too. The casein is left with the curds. (Casein is a milk protein that some people cannot tolerate.)