A gas chromatographic-mass spectrometric study of a mixture of the stereoisomers of perhydroanthracene (PHA) and perhydrophenanthrene (PHP) has been carried out. Separation was accomplished on capillary columns filled with graphitized thermal carbon black. The stereospecific features of the fragments of PHA and PHP are related, in particular, to the intramolecular repulsion of the H...H pairs of the side rings and evidently arise from the low energy of the ionizing electrons. The effect of this interaction is more clearly shown in the fragmentation of PHP, which is related to the angular disposition of the side rings, and which decreases as the structure of the isomers of the molecules becomes flatter. The predominant fragmentation paths, leading to a reduction in tension, arising from the intramolecular repulsion of the H...H pairs, are different for PHA and PHP. The fragmentation of PHA is characterized by the preferred rupture of the bonds of the side rings, while the fragmentation of PHP proceeds through the rupture of the bonds of the middle ring.