Originally Posted by http://www.toledoaasr.com/Kitchen/stains.htm

Perspiration - Sponge fresh stain with ammonia; old stain with vinegar. Pre-soak in cold or warm water. Rinse. Wash in hottest water safe for fabric. If fabric is yellowed, use bleach. If stain still remains, dampen and sprinkle with meat tenderizer, or pepsin. Let stand 1 hour. Brush off and wash. For persistent odor, sponge with colorless mouthwash.
Fresh perspiration is acid. Use a solution of alkaline to remove. Baking soda is alkaline. Old perspiration stains are alkaline. Use a milk solution of white vinegar to remove.