The baroclinic stability of a Margules front over steep topography is studied in an attempt to explain some wavelike features observed on the shelf water/slope water front south of New England. During winter this front extends from the bottom near the 85-m isobath to the surface with a typical mean slope of 2¿f10-3, with a corresponding geostrophic shear of about 10 cm/s. A quasi-synopic hydrographic survey of the New England shelf made during March 1974 resolved a wavelike distortion of the front characterized by a 80-km alongshelf wavelength. The associated Rossby number based upon the alongshelf wave number and the vertical shear (Ro=k (ΔU)/2F) is <0.05, so that a perturbation analysis using the semigeostrophic approximation is possible. This approach allows the resulting equations to be cast into an ordinary eigenvalue problem which can be easily solved numerically. The effect of increasing the bottom slope is to destabilize some neutral modes and to stabilize other modes that had been unstable over flat topography. In general, however, the characteristic &igr;e folding times of the unstable modes increase dramatically from 2--5 days for flat topography to greater than 50 days for realistically steep topography. This rapid decrease in growth rates with increasing bottom slope implies that the observed wavelike features on the front must be generated by some mechanism other than local baroclinic instability. Once they are generated, the observed features may propagate as essentially stable frontal wave modes. We note, however, that the front would be quite unstable if it was located over flat topography. This may help explain why persistent fronts of this type appear to be found near the shelf break.