This paper considers the simulation-based analysis of dispatching rules for scheduling in dynamic job shops taking into account interruptions on the shop ¯oor. With respect to ¯owtime and due date-based objectives, the relative performance of well-known, recently proposed as well as some new dispatching rules is evaluated for dierent settings of the model parameters. The results of the simulation study reveal that the relative performance of scheduling rules can be aected by changing the levels of the breakdown parameters. For the standard model, where all machines are continuously available, as well as for the models taking into account breakdowns of machines, it is shown that for minimizing mean ¯owtime the performance of one recently proposed rule (PT+WINQ) is signi®cantly better than the performance of all other rules. Analogously it is shown that for minimizing maximum ¯owtime, and for minimizing variance of ¯owtime, one new rule (AT À RPT) is superior to all other rules. With respect to due date-based objectives the relative performance of the analyzed scheduling rules is more sensitive to the percentage of time the machines have failures and the mean time to repair.