Hi, I've got an old code which works in MPICH1 (or 2). Now, I try to use MPICH3 . I've compiled MPICH3.2.1 with: env F77_GETARGDECL=" " CC="gcc" CXX="g++" FC="gfortran -ff2c -fno-second-underscore" ./configure --with-pm=hydra:gforker:remshell --enable-f90 --enable-f77 --enable-sharedlib --prefix=$HOME/mpich3 and then used it to compile the old code (MCNPX). When I run, $ ~/mpich3/bin/mpirun -np 5 -f machines ~kinyip/v270/bin/mpich3/mcnpx i=ptest n=ptest1. I've always got the error : bad trouble in mcnpx in routine getexm invalid number of command line arguments - use mpirun. It seems that it doesn't understand the "argument" above, which is " i=ptest n=ptest1. ". The gfortran does understand getarg etc. (otherwise, it'd not work with MPICH1). Do you have any advice to solve the "argument" problem.?? Kin