 Hartman split the following season between Buffalo and their AHL affiliate, the Rochester Americans, before becoming a full-time NHL'er in 1988–89.That season, Hartman racked up a career-high 316 penalty minutes and added 8 goals.The 1989–90 season proved to be Hartman's best statistically, as he scored a career-high 11 goals and 10 assists and led the Sabres in penalty minutes for the second straight year with 211.