Roy Halladay went through a vigorous bullpen session Tuesday before the Phillies played the Mets.
Philadelphia pitching coach Rich Dubee said the right-hander threw 56 pitches, stopping to simulate rest between innings.
He could have several more bullpen sessions before pitching a few simulated games.
Halladay has been out since May 28 because of a strained latissimus dorsi muscle on the right side of his back.
Halladay Throws Bullpen Session, Shows Progress