The influence of an externally applied electric field on spectral holes burned in the inhomogeneously broadened absorption bands of OEP (octaethylporphyrin) and of chlorin (2,3-dihydroporphyrin) in a PVB (poly(vinyl butyral)) matrix at 1.7 K is presented. For both molecules a linear Stark effect is observed. In the case of OEP, the linear Stark effect is caused by the interaction of the matrix-induced dipole moments and the externally applied electric field. For chlorin the effect results from molecular dipole moments as well as from the matrix-induced dipole moments. The analysis of the experimental data is based on a theory which involves the dipole moments, the polarizabilities, and the transition moments of the guest molecules, the guest-host interaction, and the macroscopic parameters of the experiment.