We construct K
-band light curves for nine field L and T brown dwarfs using the Palomar 60 inch Telescope. Results of a robust statistical analysis indicate that about half the targets show significant evidence for variability. Two of these variable targets have marginally significant peaks in the Lomb-Scargle periodogram. The phased light curves show evidence for periodic behavior on timescales of about 1.5 and 3.0 hours.