  We have evaluated the observational constraints on the spectral index $n$, in
the context of a $\Lambda$CDM model. For $n$ scale-independent, as predicted by
most models of inflation, present data require $n\simeq 1.0 \pm 0.1$ at the
2-$\sigma$ level. We have also studied the two-parameter scale-dependent
spectral index, predicted by running-mass inflation models. Present data allow
significant variation of $n$ in this case, within the theoretically preferred
region of parameter space.
