The Mn 3s multiplet splitting for a series of Mn overlayers on Ru(001) has been measured with synchrotron radiation photoemission spectroscopy. These overlayers were prepared by vapor deposition of Mn onto a Ru(001) substrate at a monolayer/minute dosing rate at room temperature. Under these conditions, the Mn overlayers grow pseudomorphically to multilayer coverages. It is found that this system exhibits a noticeable increase in the Mn 3s multiplet splitting and a positive binding energy shift as the coverage increases from monolayer to multilayer (12 ML). These results are attributed to the increase in the atomic volume, and hence the local magnetic moment at the Mn site on the average, with increasing coverage.