There are a few things to look at:

1. Water practices. Peace lilies need to be kept evenly moist. They absolutely do not like to be soggy. Try watering your peace lily on a weekly basis.
2. Chlorine is sometimes a problem for peace lilies. Water with distilled water or let your tap water sit over night before watering.
3. Hot bright light beating directly on the leaves is not a good idea.

Check to see if any of those situations are occurring. Peace Lilies are pretty tough; if you correct the problem they should recover.

As for outdoor use — I would recommend under a cover patio or a sunroom. They don’t like extreme temperatures.

For more information Flower Shop Network has a newsletter called Caring for peace lilies with some good information.

go to

http://www.flowershopnetwork.com/pages/newsletter/NewsletterMarch2003.php

Hope this helps

Jamie