Tried various forms of DB_HOST with no luck. Changing DB_HOST doesn’t change the underlying fact that the connection to mysql4 is being made using mysql3 libraries. Not advisable and very likely the cause of the “Error establishing a database connection” result. The obvious fix is to change the PATH and LD_LIBRARY_PATH of the httpd server so PHP and WP can inherit the correct settings but this will likely adversely affect other applications running on this server, so no can do. I’m grasping at straws at this point in hopes that some very seasoned WP guru will have some way of having just the WP PHP use different libraries than the host httpd.