Through the first half of 2009, ad pages in B2B publications slipped 30.2% compared with the same period in 2008, according to American Business Media's Business Information Network. For June, ad pages were down 32.8% from the same month last year.

Year-to-date, total ad revenues have dropped 26.5%, to $3.7 billion, reports Media Buyer Planner.

American Business Media tracks 21 categories, and all of them saw ad pages slip by double digits (pdf).

Faring the worst were transportation and logistics (down 54.7%), computing, telecom and software (-40.7%), electronic engineering (-36.7%), engineering and construction (-35.8%), movies, radio, TV and video (-32.5%), banking, finance and insurance (-32.5%), automotive (-32.4%), and retail (-31%).

Healthcare, the largest category tracked by ABM, was down 30.9%.

B2B trade show revenue has also declined, down 18.6% from the same period last year. Combined, trade show and business magazine revenue was down 22.3%.

Some B2B publishers are putting properties up for sale in the face of the industry's struggles. Others are shuttering publications. Reed-Elsevier put most of the magazines in its Reed Business Information group up for sale, while Nielsen closed down Radio & Records. AdAge went from 50 to 44 issues per year, and PR Week went monthly.