US internet advertising revenues fell during the first three months of the year to $5.5 billion (£3.4 billion), according to the latest figures from the Internet Advertising Bureau (IAB).
The trade group said the figure reflects a five per cent drop on the same period as last year and demonstrates that the sector has become part of mainstream marketing, which is not "immune" to broader economic trends.
Nevertheless, the IAB said interactive advertising remains in a healthier state than many other sectors of the media and it is likely to recover quickly once the US economy turns around.
IAB chief executive Randall Rothenberg said internet marketing remains the "most accountable way to reach consumers".
David Silverman of PricewaterhouseCoopers Assurance, which helped the IAB compile its figures, added that despite the "challenging" economic conditions, interactive marketing now accounts for a "larger piece of the overall advertising pie".
Figures for 2008 from the IAB show US online advertising revenues topped $28 billion.
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