  We present Spitzer IRAC (3.6, 4.5, 5.8, 8.0 um) and MIPS (24 um) observations
of the SCUBA submillimeter sources and uJy VLA radio sources in a 5'x5' area in
the Lockman Hole East region. Out of the ~40 SCUBA/VLA sources in the field,
Spitzer counterparts were detected for nearly all except for the few low-weight
SCUBA detections. We show that the majority (80-90%) of the detected sources
are cold (i.e., starburst-like) infrared-luminous galaxies (L_{IR} > 10^{11}
Lsun) at redshift 0.5<z<3.5, whose star-formation rate density (SFRD) is
comparable to that of the optically-selected star-forming galaxies.
