Mold can be worse than unsightly and a bad smell, it can also be toxic black mold otherise known as Stachybotrys. If you suspect that you may have a mold problem in your house, there are tests available to detect its presence.
Visit your local hardware store. You can find home mold detection kits that allow you to take samples where you see mold, test your furnace and air samples. Generally, you will put these samples in a safe place for 48 hours and the kit will include directions so you can determine the results at that time.
Order a kit online. There are a few great sources for mold testing kits. Some kits are far more in depth than others so you can choose what you feel is best for your situation. If you would prefer that a professional review the results, there are also kits that include overnight service back to their lab where they will determine the results for you. Please see below for a list of links that may be of assistance.
Contact a professional for a consultation in your home. Simply go to yellowpages.com and type in a search for Mold Testing & Consulting and your zip code and you should have many choices in the area for someone who will come to your home and perform testing for you.