The angular distribution of particle velocities in a magnetized plasma can be uniquely determined by measurement of the variation of density along a magnetic field line. From measurements on the 2XII mirror experiment, it is determined that the angular distribution of ions is monotonic and very closely approximatessin2a&thgr;,wherea = 2.25and&thgr;is the pitch angle at the center. Particles with sin&thgr; < 0.72communicate with the region outside the mirrors and comprise approximately 5&percent; of the total density at the center.