Electric-field modulation considerably enhances structure in the reflectance of a solid. In addition to the greater sensitivity, the symmetry-breaking effect of the modulation parameter provides symmetry information useful in the identification of critical points. Interband transitions, excitonic excitations and interactions between carriers and lattice can, in principle, be evaluated in their relative contributions to the optical absorption process. The present status of theory and experiment is briefly reviewed in this respect. So far few electroreflectance measurements have been performed on IV-VI compounds. As for all other materials the existing structure in static optical measurements is enhanced. Some new structure does not relate to formerly observed transitions. Properties characteristic for IV-VI compounds make measurements and interpretation of their electroreflectance spectra difficult. A high-carrier concentration results in compressed space-charge layers which are smaller than the penetration depth of the reflected light. This requires a modified analysis. A large dielectric constant distorts the waveform through phase-lags between modulation and response. Weak nonaqueous electrolytes required in the infrared and in the presence of soluble substrates add parasitary space-charge effects. All these factors complicate quantitative line-shape discussions. At present, a critical-point analysis can only be tentative ; however, some of the experimental results can be correlated to existing band-structure calculations and, in general, support their claims. Some features of the experimental results suggest that electroreflectance in degenerate IV-VI compounds, such as SnTe, is not a critical-point phenomenon. Spectra of the mixed-crystal series PbxSn1-xTe change from one type at one end to a markedly different type at the other. Although still enhancing the structure of static optical techniques, electroreflectance is probably restricted as a critical-point phenomenon in these degenerate materials