We observed the field of GRB 100305A (Troja et al., GCN 10470) with the 1.3m PAIRITEL located at Mt. Hopkins, Arizona. Observations began at 2010-03-05 09h29m30s UT, ~0.4 hours after the Swift trigger.  In initial mosaics (effective exposure time of ~795.6 seconds) taken simultaneously in the J, H, and Ks filters, we do not detect any sources within the XRT error circle. The preliminary photometry yields: post_burst t_mid(min)  exp(s)  filt    U. Limit (3 sig) 34.6        795.6  J       > 19.2 34.6        795.6  H       > 18.0 34.6        795.6   Ks      > 17.3 Observations are ongoing.  All magnitudes given in the Vega system, calibrated to 2MASS.  No correction for Galactic extinction has been made to the above reported values.