Results of an organic petrographic study of the Kupferschiefer (Zechstein, Upper Permian) in northern Germany are presented. Because vitrinite occurs only sporadically in this black shale, the random reflectance (R-r) of a relatively high reflecting, vitrinite-like variety of bituminite was measured as a maturity parameter and the problems connected with this procedure were investigated. The main organic component is bituminite, generally with an abundance of more than 90%. Sporomorphs and algae are relatively scarce, inertinite is usually a trace component, and vitrinite is present only in some samples taken close to the coast of the Zechstein sea. Migrabitumen also occurs in small amounts in a few samples. The range of the bituminite reflectance values is often considerable and depends on rank, anisotropy, particle size, porosity, and shearing. Interpretation of the reflectance values is made difficult by differences of up to 0.4% R-r between layers within the Kupferschiefer. Hydrothermal alteration may also be present. The difference between the reflectance of the light and normal varieties of bituminite disappears between 0.9 and 1.2% R-r. Bituminite behaves in a way very similarly to vitrinite during coalification. Their reflectance is identical between 2 and 4% R-r. Below 2% R-r, the reflectance of bituminite is lower than that of vitrinite. Linear regression curves valid up to 4% R-r were calculated for R-max versus R-r and for R-r versus R-max. Taking certain limitations into consideration, bituminite reflectance may be used as a coalification parameter.