Dear colleagues, I would like to have your advice on how to call C from Fortran. Essentially I have a Fortran program for numerical optimisation that often uses object function as its function/subrouine arguements. However, it appears most examples of F77_SUB concern about arrays/matrices and not function -- I could work directly with C with help of f2c but it would be very nice to keep the familiar Fortran code intact. I have tried to remove the argument and keep it in an Fortran EXTERNAL statement. The Fortran routine is appealing to me as it handles nonlinear constraints. I tried to work it out like this: use .Call from R to call a C wrapper which processes the environment and parses R expressions, use F77_CALL to call the Fortran routines which in turn uses an objective function in C -- I use global variables to pass the environment and R function from the C wrapper to C objective function. I have problem with F77_CALL, however. This sounds a bit confusing though simple conceptually. I am grateful of any example or idea. Many thanks, Jing Hua