The Houston Astros drafted eighteen-year-old Mizerock straight out of Punxsutawney High School in Punxsutawney, Pennsylvania. He was the second of five catchers selected in the first round of the June draft. After four seasons in their farm system, in which he batted .228 with eighteen home runs (twelve of which were hit in ) and 143 runs batted in, Mizerock made the Astros out of Spring training as Alan Ashby's back-up. He allowed three passed balls in a game against the Cincinnati Reds on April 19 to not only lose the back-up catcher job, but to also get himself sent back down to the minors. In fairness to Mizerock, knuckleballer Joe Niekro was pitching.