The figure was in line with analysts' predictions, but was a drop from the 6% growth reported in a quarterly trading statement in April.
The group's chairman Sir Martin Sorrell said that revenues for the five months to May 31 were up 69%, chiefly reflecting the acquisition of Young & Rubicam, which WPP bought in October 2000 for around $3.9bn (£2.7bn) in stock.
However, excluding acquisitions and the impact of currency, like-for-like sales rose almost 4%. "This is significantly less than the comparable growth rate of 15% for the calendar year 2000 and reflects the impact of the US business-to-business recession which started in the fourth quarter of 2000," Sir Martin said.
Worst hit by the slowdown were the company's public relations and public affairs businesses, followed by branding, identity, healthcare and specialist communications. Advertising, media investment management, consultancy and information were relatively unscathed.
Geographically, the US market remains most affected, although the impact is being felt in Europe, Asia Pacific and Latin America, he said.
Sir Martin added that the group was in line to improve its operating margins to 15% in 2001 and 15.5% in 2002. The longer-term margin target remains 20%.
WPP closed last night at 676p and had fallen to 668p in early trading this morning.