Fresh mushrooms will keep for 10-14 days in the fridge, although may last for less time if they were sat in the supermarket for sometime before purchasing. If you're not sure if your mushrooms are going off then there are a few things you can do to tell if they are past their best:
• Check for brown spots or areas where the flesh has darkened and the texture is turning very soft.
• Make sure that they don't smell odd. Mushrooms naturally have a slight odour but if you can smell it from a distance or it smells particularly strong then don't use them
• Touch the mushrooms and if they feel slimy or very wet to the touch then they are definitely past their best.