  We present a multiwavelength study of the infrared dark cloud MSXDC
G034.43+00.24. Dust emission, traced by millimeter/submillimeter images
obtained with the IRAM, JCMT, and CSO telescopes, reveals three compact cores
within this infrared dark cloud with masses of 170--800 Msun and sizes < 0.5
pc. Spitzer 3.6-8.0 um images show slightly extended emission toward these
cores, with a spectral enhancement at 4.5 um that probably arises from shocked
H2. In addition, the broad line widths (Delta V ~ 10 km/s) of HCN (4-3), and CS
(3-2), and the detection of SiO (2-1), observed with the JCMT and IRAM
telescopes, also indicate active star formation. Spitzer 24 um images reveal
that each of these cores contains a bright, unresolved continuum source; these
sources are most likely embedded protostars. Their millimeter to mid-IR
continuum spectral energy distributions reveal very high luminosities,
9000-32,000 Lsun. Because such large luminosities cannot arise from low-mass
protostars, MSXDC G034.43+00.24 is actively forming massive (~ 10 Msun) stars.
