  We confront Cardassian models with recent observational data. These models
can be viewed either as purely phenomenological modifications of the Friedmann
equation, or as arising from cosmic fluids with non-standard properties. In the
first case, we find that the models are consistent with the data for a wide
range of parameters but no significant preference over the Lambda-CDM model is
found. In the latter case we find that the fact that the sound speed is
non-zero in these models makes them inconsistent with the galaxy power spectrum
from the Sloan Digital Sky Survey.
