 In 1988, he moved up to middleweight, suffering his first defeat, a clear unanimous decision, in an attempt to win the WBA middleweight championship from Sumbu Kalambay.In 1989, McCallum defeated Herol Graham by a split decision to win the then-vacant WBA middleweight title (which had been stripped from Kalambay for signing to face IBF champion Michael Nunn).He defended the title three times, defeating Steve Collins, Michael Watson, and Kalambay in a rematch.