Motivated by recent studies of the one-bubble inflationary scenario , simple open cold dark matter models are tested for consistency with cosmological observations .
The initial perturbation spectrum is derived by solving for the evolution of fluctuations in an open inflationary stage .
A likelihood analysis is performed for the Cosmic Microwave Background anisotropies using the two-year COBE DMR data and considering models based on both the Bunch-Davies and conformal vacua .
Having normalized the perturbation spectrum to fit the COBE data , we reconsider the validity of the open model from the view point of cosmic structure formation .
Open models may be severely constrained by the COBE likelihood analysis .
In particular , small values of \Omega _ { 0 } are ruled out in the Bunch-Davies case : we find that \Omega _ { 0 } \geq 0.34 at 95 % confidence for this model .

Subject headings : cosmology : theory — cosmic microwave background — large scale structure