  We study the possible contribution of a stochastic gravitational wave
background to the anisotropy of the cosmic microwave background (CMB) in cold
and mixed dark matter (CDM and MDM) models. We test this contribution against
recent detections of CMB anisotropy at large and intermediate angular scales.
Our likelihood analysis indicates that models with blue power spectra ($n
\simeq 1.2$) and a tensor to the scalar quadrupole ratio of $R = C_2^T /C_2^S
\sim 2$ are most consistent with the anisotropy data considered here. We find
that by including the possibility of such background in CMB data analysis it
can drastically alter the conclusion on the remaining cosmological parameters.
