Natural programs can call COBOL subroutines. Use the “CALL” statement instead of CALLNAT. Natural uses the calling conventions of the environment that it is running in. Thus, if you want to CALL ‘CBLRTN’ from Natural in TSO or batch, the called routine must be compiled as a standard (not CICS) routine; if you want to call it from Natural in CICS, then “CBLRTN” must be defined to the PPT and use CICS calling conventions (COMMAREA for parameters).
There are examples provided in the documentation and SYSEX* libraries.
(There is an alternative for CICS to call routines using standard linkage rather than CICS linkage - I don’t recommend it particularly, but it is documented in the Natural documentation).