We study the anisotropy of the cosmic microwave background ( CMB ) in cold and mixed dark matter ( CDM and MDM ) models , with non scale-invariant primordial power spectra ( i.e . n \neq 1 ) and a late , sudden reionization of the intergalactic medium at redshift z _ { rh } .
We test these models against recent detections of CMB anisotropy at large and intermediate angular scales .
We find that current CMB anisotropy measurements can not discriminate between CDM and MDM models .
Our likelihood analysis indicates that models with blue power spectra ( n \simeq 1.2 ) and a reionization at z _ { rh } \sim 20 are most consistent with the anisotropy data considered here .
Without reionization our analysis gives 1.0 \leq n \leq 1.26 ( 95 \% C.L . )
for \Omega _ { b } = 0.05 .