This command is only applicable under CICS.

%QO

In a Natural session running under CICS in pseudo-conversational mode, you can switch to another CICS transaction by issuing the statement CALL 'CMTASK'. To enable CICS to start the other transaction, a terminal I/O, i.e. an INPUT statement, is required after the CALL statement.

To suppress the screen output of that INPUT statement (which would be overwritten immediately by the started transaction anyway), you issue a SET CONTROL 'QO' statement before the INPUT statement.