Little has been added to knowledge of the geochemistry of rhenium since the work of Noddack and Noddack in 1931, except that many determinations have been published of the rhenium content of molybdenite, the only present source. These determinations, 150 in all, have been assembled. The rhenium content of molybdenite ranges from none to 3,250 ppm Re, and varies widely, even in samples from a single deposit. No generalizations are yet possible as to correlations of rhenium content with geological conditions of formation. Other possible sources of rhenium are considered briefly. (auth)