To date, six computationally intense but frequently needed crystallographic applications programs have been developed for an array processor (Floating Point Systems model AP 190L) driven by a DEC 10 computer. In all of the applications attempted, it was possible to reduce the required processing time to at least an order of magnitude below that required by a large university scale computer (DEC 10) for the same problem. In fact, the rate-determining step in full-matrix least-squares refinement can be made to run 20–30 times faster in the array processor. For the refinement of proteins, one cycle with a space-group-general algorithm executes faster in the array processor than a typical small-molecule refinement cycle executes on the DEC 10. We conclude that many of the time-consuming operations frequently encountered in crystallographic computer programs can be handled very efficiently on an inexpensive array processor attached to a host computer.