In MATLAB versions up to 7.7 (2008b) you can determine the maximum number of threads that it can use with
N = maxNumCompThreads LASTN = maxNumCompThreads(N) LASTN = maxNumCompThreads('automatic')
In MATLAB versions 7.8 and onward, the maxNumCompThreads function is not supported any more. Instead, you can tell MATLAB that it should use a single thread at startup by providing the -singleCompThread to the smartup command, e.g.
matlab78 -nodesktop -singleCompThread
See http://www.mathworks.com/access/helpdesk/help/techdoc/ref/maxnumcompthreads.html for more details.