  Non-commutative inflation is a modification of standard general relativity
inflation which takes into account some effects of the space-time uncertainty
principle motivated by ideas from string theory. The corrections to the
primordial power spectrum which arise in a model of power-law inflation lead to
a suppression of power on large scales, and produce a spectral index that is
blue on large scales and red on small scales. This suppression and running of
the spectral index are not imposed ad hoc, but arise from an early-Universe
stringy phenomenology. We show that it can account for some loss of power on
the largest scales that may be indicated by recent WMAP data. Cosmic microwave
background anisotropies carry a signature of these very early Universe
corrections, and can be used to place constraints on the parameters appearing
in the non-commutative model. Applying a likelihood analysis to the WMAP data,
we find the best-fit value for the critical wavenumber k_* (which involves the
string scale) and for the exponent p (which determines the power-law
inflationary expansion). The best-fit value corresponds to a string length of
L_s \sim 10^{-28} cm.
