Users of small computers must often program in assembler language. Macros are described which assist in the construction of block structured programs in assembler language. The macros are used in practical day‐to‐day programming in a cardiac electrophysiology laboratory in which the coarse grained control provided by the local FORTRAN compiler is not sufficient for, and even hinders, the writing of clear, easy to understand programs. The macros provide nestable control structures in place of the less structured transfers of conventional assembler language. The arithmetic and input/output control provided by the architecture of the machine is left fully available. The control structures implemented include conditional (IF, CASE), iteration (WHILE, REPEAT/UNTIL, FOR) and subroutine (PROC, CALL, etc.) constructs. No control of variable scope is provided. The macro implementation is discussed along with the code generated. There is a discussion of architectural features which allow the macros to be independent of specific register usage and addressing mode. Experience with use of the macros in a high‐speed, real‐time data acquisition and display environment is presented. We conclude that these macros are easy to use and assist in program readability and documentation. Copyright © 1975 John Wiley & Sons, Ltd