The National Association of Realtors (NAR) has set policies that permit brokers to show limited MLS information on their websites under a system known as IDX or Internet Data Exchange. NAR has an ownership interest in Homestore, the company which operates a website that has been given exclusive rights to display significant MLS information. The site is Realtor.com.

Using IDX search tools available on most real estate brokers' websites (as well as on many individual agents' sites), potential buyers may view properties available on the market, using search features such as location, type of property (single family, lease, vacant land, duplex), property features (number of bedrooms and bathrooms), and price ranges. In some instances photos can be viewed. Many allow for saving search criteria and for daily email updates of newly-available properties. However, if a potential buyer finds a property, he/she will still need to contact the listing agent (or their own agent) to view the house and make an offer.

The U.S. Department of Justice filed an antitrust lawsuit in September 2005 against the National Association of Realtors over NAR's policy which would have allowed brokers to restrict access to their MLS information from appearing on the websites of certain brokers which operate solely on the web. This policy would also have applied to commercial entities which are also licenced brokerages, such as HomeGain, which solicit clients by internet advertising and then provide referrals to local agents in return for a fee of 25% to 35% of the commission.

The DOJ's antitrust claims also include NAR rules that exclude certain kinds of brokers from membership in MLSs. NAR has revised its policies on allowing access on web sites operated by member brokers and others to what might be considered as propriety data.