New York--DoubleClick, New York, a leader in serving broad-based Internet advertising campaigns, said Thursday that it has invested $85 million in ValueClick, Carpinteria, Calif., in exchange for a 30% equity stake. The move is significant because it establishes a beachhead for DoubleClick in the cost-per-click advertising model. Under terms of the agreement, ValueClick will integrate DoubleClick's software and services for delivering and tracking Internet advertising--dubbed DART--into its own ad-serving network. In so doing, DoubleClick will be able to point cost-per-click campaigns to ValueClick, while ValueClick will be able to direct broader campaign business to DoubleClick. Cost-per-click campaigns are of interest to business marketers, who are often more interested in advertising that acquires a passel of high-value relationships than they are in broad messaging. Even with DoubleClick as an ally, ValueClick has its work cut out. Flycast Communications Corp., San Francisco, recently added a cost-per-click offering, and the emerging business-to-business advertising specialist B2BWorks, Chicago, will also likely focus much of its effort on performance-based advertising. Internet advertising is expected to grow from a $1.5 billion market in 1998 to more than $22 billion by 2004, according to Forrester Research, Cambridge, Mass.