Maybe Fido curled up in a warm basket of clean laundry and had an accident, or maybe Max snuck into your bed and left you a surprise. Cleaning pet stains and odors is a chore when they're on the floor, but when they get on clothing, bedding or laundry, it often takes a multistep process to fully eradicate the smell.
Don’t Let It Set
It can be easy to wad up soiled laundry and set it aside to deal with later, but tackling the problem right away will give you better odds at success. Rinse the soiled items in cold water, and then put them in the washing machine. Fill it up and add a 1-pound box of baking soda to your usual detergent. Run the cycle as usual.
Give It a Sniff
Smell the laundry items once they've gone through a wash cycle. If you can still smell traces of urine, repeat the wash cycle using an enzymatic cleaner instead of baking soda and detergent. Follow the directions on the bottle -- it may suggest you run a soak cycle so the enzymes can do their job.
Let It Dry
When you're convinced the urine is gone, air-dry your laundry -- don't use the dryer. Smell the items once they're dry and go through the steps once again if urine odor remains.
If your dog urinates on something heavy, like a comforter, you may be better served going to a commercial laundromat where you can use an oversize washing machine. Another option is dry cleaning -- commercial cleaners often can apply special agents to remove smells. Call in advance and ask if they specialize in removing pet odors.
Keep laundry away from your dog. Make sure dirty clothes end up in hampers rather than on the floor, and don't let clean laundry sit around where your dog can access it.