Serving advertisements with (e.g., in) audio documents may be improved by (a) accepting at least a portion of a document including audio content, (b) analyzing the audio content to determine relevancy information for the document, and (c) determining at least one advertisement relevant to the document using at least the relevancy information and serving constraints associated with advertisements. The advertisements may be scored if more than one advertisement was determined to be relevant to the document. Then, at least one of the advertisements to be served with an ad spot for the document may be determined using at least the scores. Examples of documents include radio programs, live or recorded musical works with lyrics, live or recorded dramatic works with dialog or a monolog, live or recorded talk shows, voice mail, segments of an audio conversation, etc. The audio content may be analyzed to determine relevancy information for the document by converting the audio content to textual information using speech recognition. Then, relevancy information may be determined from the textual information.