A theoretical description of the quantum electromagnetic field in the lipid-water system is presented, and the spontaneous emission rate of an excited molecule bound in the lipid layer is calculated. By using the reflectivity data of liquid water, the emission rates as a function of the wavelength and the index of refraction of hydrocarbon are calculated. Depending on the alignment of the transition dipole, the spontaneous emission rate is found to be modified significantly. When the alignment of the transition dipole is perpendicular to the lipid-water interfaces, the emission rate is more strongly suppressed by the presence of the boundaries, in comparison to the parallel case. It is suggested that one could experimentally measure this alignment dependence of the spontaneous emission process in the lipid-water system, and some possible implications to the antenna system in the photosynthesis are briefly discussed. (C) 1997 American Institute of Physics.