ROTATION PERIODS OF OPEN-CLUSTER STARS .2.

We present the results from a photometric monitoring program of 21 sta rs observed during 1992 in the Pleiades and Alpha Persei open clusters . Period determinations for 16 stars are given, 13 of which are the fi rst periods reported for these stars. Brightness variations for an add itional five cluster stars are also given. One K dwarf member of the a lpha Per cluster is observed to have a period of rotation of only 4.39 hr, perhaps the shortest period currently known among BY Draconis var iables. The individual photometric measurements have been deposited wi th the NSSDC. Combining current X-ray flux determinations with known p hotometric periods, we illustrate the X-ray activity/rotation relation among Pleiades K dwarfs based on available data.