This investigation is concerned with the possibility of identifying viral DNA using the in situ DNA hybridization method in methylmethacrylate-embedded material. As an experimental model we chose viral labyrinthitis produced by intranasal infection of the mouse with pseudorabies virus. Fixation and embedding methods specially adapted to this procedure and bony histology preparation technique (specimens by grinding or micromilling) made it possible to identify viral DNA directly morphologically and virologically in the inner ear. Quantitative microphotometric analyses of trans-sagittal sections of the entire skull after in situ DNA hybridization are presented and discussed here as an explicit method of investigating the path of distribution of viral DNA in the brain and the inner ear.