A CALL statement or a CALL macro instruction refers to an external name in the segment where control is passed. The external name must be defined as an external reference in the requesting segment. In assembler language, the name must be defined as a 4-byte V-type address constant. The high-order bit is reserved for use by the control program and must not be altered during execution of the program.

When a CALL is used, the requested segment and any segments in its path are loaded if they are not part of the path already in virtual storage. After the segment is loaded, control is passed to the requested segment at the location specified by the external name.

A CALL between inclusive segments is always valid. A return can be made to the requesting segment by another source language statement, such as RETURN. A CALL between exclusive segments is valid if the conditions for a valid exclusive reference are met; a return from the requested segment can be made only by another exclusive reference, because the requesting segment has been overlaid.