Pre-treat underarm area of garment with a liquid laundry detergent so the buildup can be washed away. If the stain is old, treat with white vinegar to help dissolve any old perspiration. Wash in hot water every few washes to help remove sweat buildup.
If the deodorant has been sitting for a while, you should apply diluted white vinegar to the affected area, allowing it to sit for approximately half an hour. Rinse vinegar from the fabric and apply prewash stain treatment. Launder in the hottest water the fabric allows.