We propose a methodology for assessing how ad campaigns in offline media such as print, audio and TV affect online interest in the advertiser's brand. Online interest can be measured by daily counts of the number of search queries that contain brand related keywords, by the number of visitors to the advertiser's web pages, by the number of pageviews at the advertiser's websites, or by the total duration of visits to the advertiser's website. An increase in outcomes like these in designated market areas (DMAs) where the offline ad appeared suggests heightened interest in the advertised product, as long as there would have been no such increase if the ad had not appeared. We propose a regression analysis to estimate the incremental value of the ad campaign beyond the baseline interest that would have been seen if the campaign had not been shown. A small print ad campaign illustrates the method.