The dark matter distribution of the Milky Way remains among the major unsolved problems about our home galaxy .
The masses of other spiral galaxies can be determined from their rotation curves through long-slit spectroscopy .
But for the Milky Way obtaining the complete rotation curve is a more complex problem .
By measuring the 3-dimensional motions of tracer objects the rotation curve and Galactic mass distribution can be derived , even outside the solar circle where H _ { I } tangent point analysis is not possible .
We present the first findings from a project to measure the motions of open clusters , both inside and outside the solar circle .
From a nearly uniform sample of spectroscopic data for large numbers of stars in over 50 open clusters in the third and fourth Galactic quadrants , we derive the speed of Galactic rotation at the solar circle as \Theta _ { 0 } = 214 ^ { +6 } _ { -9 } km s ^ { -1 } .
Future work will include clusters in the other Galactic quadrants and analysis of the local rotation curve .