Google announced a new feature of AdWords v2009 API, called “Ad parameters,” that enable you to change numeric information (for example: prices, discount percentages, etc.) within your text ad, while keeping history and statistics associated with ad. Notice that you can specify default values for param1 and param2 within the ad text. You need to set dynamic numeric values for param1 and param2 at the keyword level via AdParamService of v2009 API, noted API blog.
With Ad parameters, you can specify ad like this: User searching for "antique cups" will see following ad:
Full Article: API blog