Beginning with the R2009a release of MATLAB, .NET objects can be accessed from MATLAB:
http://www.mathworks.com/help/techdoc/matlab_external/brpb5k6.html
In older versions of MATLAB, it is possible to access .NET objects from MATLAB using CCW:
http://www.mathworks.com/support/solutions/data/1-5U8HND.html?solution=1-5U8HND
and the MATLAB engine from .NET:
You can also use the MATLAB Builder NE to wrap m-code into .NET assemblies.