Many assembly systems are required to hold minimal work-in-process inv
entories because of space or capital limitations. Unfortunately, in th
e presence of variable processing times, output from an assembly line
may be severely restricted if no work-in-process inventory is held. Th
us, assembly lines often should be designed to have minimal, but not z
ero, buffer capacity. In this paper we address the issue of how one sh
ould optimally deploy limited buffer capacity in unbalanced assembly s
ystems, and we find that the answer is sometimes counterintuitive. We
study simple asynchronous assembly systems with random processing time
s and develop simple heuristic rules that can be used to improve exist
ing operations and to support line designers who are faced with increa
singly rapid cycles of new product introduction. We apply these heuris
tics to several larger systems and discover that they perform quite we
ll.