Garbage collection can be done in vector mode on supercomputers like the Cray-2 and the Cyber 205. Both copying collection and mark-and-sweep can be expressed as breadth-first searches in which the "queue" can be processed in parallel. We have designed a copying garbage collector whose inner loop works entirely in vector mode. We give performance measurements of the algorithm as implemented for Lisp CONS cells on the Cyber 205. Vector-mode garbage collection performs up to 9 times faster than scalar-mode collection --- a worthwhile improvement. - 1. Automatic garbage collection on vector supercomputers Languages like Lisp with dynamic storage allocation and automatic garbage collection are increasingly being used on vector supercomputers. Implementations of Lisp have been done for Cray supercomputers [1], and fully supported supercomputer Lisp environments will soon be available (e.g. Common Lisp provided by Cray Research and Franz, Inc.)[2]. This is a natural development. Languages ...