A description of a block-programming facility that Rand has incorporated into the basic IBM-360 software. This new facility alters the form of the machine language enough to change the way programmers conceive of and code problems. By means of a set of macros, users can write a program as a hierarchical set of instruction blocks whose execution is controlled by conditional statements, thus providing, at the assembly code level, the IF-THEN-ELSE facility of ALGOL and PL/I. Other conditional statements can occur within an IF block. A formatting program automatically indents the program listing to reflect its structure and provides headings for the beginning and end of each block, adding greatly to program readability and self-documentation. Lines added by the program are immediately recognizable because the line numbers are suppressed, distinguishing them from lines produced by the O/S assembler. 9 pp.