Hi Lisa,

Here is an answer I found doing a search on the subject:

Here is a link that might be useful: Perspiration stain removal

thanks for that link...i found that the vinegar helped for a while....and i didn't know about the ammonia thing....will try that on new stains....

and i suppose that i might just have to break down and buy a few new shirts once in a while! :D

I think I would try the process I use on badly stained tablecloths and napkins. Set washing machine on hot water and the lowest level of water. Add 1 cup of Clorox liquid bleach, 1 cup of detergent and 1 cup of electric dishwasher detergent. Agitate it and add the clothes. Agitate briefly. Turn off machine and let clothes soak overnight. In the morning, turn the machine on and run it through a cycle. That should take care of the stains. If you are nervous about using a liquid chlorine bleach, try the soak and wash with just the two detergents. Do not put the clothes in the dryer if the stain is still there--run the soaking and wash process till stain is removed. Usually one treatment gets all my stains out.

Mama's Miracle Linen Soak. It's the best I've found for removing all sorts of stains. It says it's for vintage and antique fabrics, but it works just as well on new ones. You can buy it on Amazon or at mamasmiracle.com.