The vibrational Stark effect of a series of small molecules has been calculated by means of the semiempirical AM1 method through addition of the electron–field interaction term in the one‐electron Hamiltonian. Optimized geometrical parameters along with harmonic frequencies and line intensities are determined for different strengths of the applied uniform electric field. The perturbed spectra are compared with theoretical studies carried out at the ab initio level and with experimental results. The vibrational Stark effect of the retinal molecule is also computed, showing that this kind of study is feasible in systems of biochemical interest. © 1992 by John Wiley & Sons, Inc. Copyright © 1992 John Wiley & Sons, Inc.