Some general guidelines are discussed on why and how to develop utility functions in assembler for the APL2/PC environment. Assembler utility functions may replace some most heavily used idiomatic APL auxiliary functions and boost the effkiency of APL applications. About twenty such functions are presented, some of them perhaps useful astemporary extensions of the APL2/PC interpreter. The collection of assembler utility functions is available in the public domain, and should be extended by the joint efforts of the international APL community.APL2JPC offers several auxiliary processors for different purposes aswell as tools for writing one's own auxiliary processors. One of the auxiliary processors supplied is AP2, the Non-APL Program Auxiliary Processor. It is designed to load and execute non-APL programs, either through the DOS command interface, or directly, as APL functions. The latter is an almost ideal (not quite, due to the 64 k restriction!) interface for running assembler subroutines that meet the above-mentioned criteria.Assembler Utility Functions 358 APL 91