The exciton fine structure of the fundamental absorption edge in semiconductor crystals was examined. It was observed that substances having such a structure are fairly strong photo-conductors. This fact leads to the conclusion that there is a correlation between the exciton absorption lines and the shape of the photoconductivity curve. Crystals with well-known structures of the absorption edge (CdS, Cu 2O, HgI 2, PbI 2 and GaSe) were chosen for investigation. A fine structure of the spectral curves of photoconductivity, corresponding to exciton absorption lines, was discovered in all the investigated crystals at low temperatures. Its properties in a CdS single crystal were studied in detail. It turned out that either the maxima (first type of crystals) or the minima (second type of crystals) on the photocurrent curves could correspond to the exciton absorption lines. By means of proper treatment crystals can be converted from one type into another and vice versa. The coincidence of photocurrent and absorption maxima is considered as a consequence of exciton participation in giving rise to photocurrent. Possible mechanisms of exciton participation in creating charge carriers are discussed. On the spectral curve of luminescence excitation of CdS crystals at low temperatures, a fine structure related to the exciton spectrum is also observed. Either maxima or minima on the excitation spectral curve coincide with the exciton absorption lines.