How many innings were in the longest pro. baseball game in history which two future hall of famers played in this game?

33.

The longest game in American professional baseball history was started on April 18, 1981 between the Pawtucket Red Sox, a triple A minor league affiliate of the Boston Red Sox, and the Rochester Red Wings who were a triple A affiliate of the Baltimore Orioles, at McCoy Stadium in Pawtucket, Rhode Island. The future Hall of Famers were Wade Boggs for Pawtucket and Cal Ripken Jr. for Rochester. The game went 32 innings and almost eight hours before it was called due to exhaustion of the players with the score tied at 2. The game ended on June 23 with just one more inning needing to be played as Pawtucket scored in the bottom of the 33rd to win 3-2.