ROTATION PERIODS OF OPEN-CLUSTER STARS .3.

We present the results from a photometric monitoring program of 15 ope n cluster stars and one weak-lined T Tauri star during late 1993/early 1994. Several slow rotators which are members of the Alpha Persei, Pl eiades, and Hyades open clusters have been monitored and period estima tes derived. Using all available Pleiades stars with photometric perio ds together with current X-ray flux measurements, we illustrate the X- ray activity/rotation relation among Pleiades late-G/K dwarfs. The dat a show a clear break in the rotation-activity relation around P simila r to 6-7 days-in general accordance with previous results using more h eterogeneous samples of GPK stars.