Selling more units at lower cost is one of the tasks advertising should perform. There is ample proof that advertising, if perceived, if read or listened to and especially if recalled does cause purchasing. Getting consumers to so react to advertising largely depends on the quality of ads and commercials. Spending money in the creative area therefore is even more important than buying space and colour. Producing attractive advertising does help to increase perception levels. The single most deciding criterion is shown to be the interestingness of advertisements. Interest causes both perception and sales effects. In auditing the effects of advertising measures of interest aroused should take its place alongside recognition, proved recall and registration of buying intentions (or if at all possible: buying behaviour). Measures of interest are particularly useful in connecting pretest to post-test-data. Findings from various ad hoc surveys and continuous post testing are reported. A plea is made to audit advertising effects in much the same way as a companys profits (or losses) are being checked. Advertising and every single ad or piece of copy should be viewed as just another product that should perform the functions it is designed for. Poor advertising should be discontinued just as quickly as unsuccessful product lines.