"At 10:31:54.97 UT on 28 July 2010, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 100728B (trigger 302005916 / 100728439), which was also detected by the Swift-BAT (Morris et al. 2008, GCN 11009) The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 57.1 degrees. The GBM light curve shows a single pulse with a duration (T90) of about 11.8 +/- 2.4 s (50-300 keV). The time-averaged spectrum from T0-1.024 s to T0+5.632 s is well fit by a power law function with an exponential high energy cutoff. The power law index is -0.9 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 131 +/- 15 keV (chi squared 1043 for 599 d.o.f.). The event fluence (8-1000 keV) in this time interval is (2.4 +/- 0.1)E-06 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+1.22 s in the 8-1000 keV band is 6.2 +/- 0.2 ph/s/cm^2. A Band function fits the spectrum equally well (chi squared 1037 for 598 d.o.f.) with Epeak= 104 +/- 14 keV, alpha = -0.8 +/- 0.2 and beta = -2.2 +/-0.2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."