I've implemented basic asynchronous communications in ocamlmpi. It's in the svn version. I'd be glad if fellow ocaml parallel programmers took a look and tested it out. Suggestions welcome, also, let me know if there is an API call you need urgently. The objective is to complete all the missing stuff from MPI-1 standard, eventually. It's incredibly comfortable to use the generic interfaces of ocamlmpi. Compared to C, it's a breeze. This addition was quite helpful in my research code, I could easily program my own all-to-all-personalized communication function :) And as you know, for achieving communication/computation overlap this is the best way to proceed, which I haven't exploited in my new parallel information retrieval application yet, but I did verify that the async. calls worked.