  We investigate the possibility of a dark energy component that is scaling
with epochs. A phenomenological model is introduced whose energy density
depends on the redshift in such a way that a smooth transition among the three
dominant phases of the universe evolution (radiation era, matter domination,
asymptotic de Sitter state) is achieved. We use the WMAP cosmic microwave
background data and the luminosity distances of Type Ia Supernovae to test
whether this data can provide a signal for scaling.
