This research program had the primary objective of developing site-specific water quality criteria for metals through correlating aquatic toxicity with activities of metal species. The project was not intended to carry out experimental studies but to make use of existing literature reports of metal toxicity to generate the correlations. This programmers manual consists of three parts: (A) Definitions and Computational Algorithms for REDEQL-UMD in which the algorithms for all computational processes are described, with examples used when the procedure is complex. (B) Parameter and Global Variables for REDEQL-UMD in which the global variables are defined as to nature and type, and normal ranges are given as well as the names of subroutines in which they are used and the kind of use made of the variables in those subroutines. (C) Flow Diagrams for REDEQL-UMD in which flow diagrams for all subroutines are given in considerable detail as well as a general flow sheet for the program. The manual will find greatest use by those desiring to make major modifications to REDEQL-UMD although it would be useful to a serious user wishing to obtain a more thorough understanding of the set of programs.