The names Niclaes van Oldenborch and Magnus vanden Merberghe van O(e)sterhout have long presented historians of the Dutch book with a problem. They appear as imprints in two series of, mostly theological, publications in the vernacular, published respectively in the third and fourth decade of the sixteenth century and in the 1550s. Owing to the attributions of Dr Kronenberg, the distinguished expert in the field, the Van Oldenborch production swelled into a list of almost forty publications, a substantial part of the Protestant works to have been issued in the period. She was convinced of the man's historicity and continued to insist on it even after serious doubts had arisen about the accuracy of the principal piece of information on which she based her views. Further research now proves that, as had already been suggested earlier, Van Oldenborch was indeed a pseudonym, used by more than one printer in Antwerp and presumably also in Kampen. A total of seven, if not of eight, publishers adopted it at various times. Vanden Merberghe, too, was a fake imprint, but only one printer seems to have concealed his identity with it: Frans Fraet in Antwerp. Hitherto he was known exclusively for his literary work, even if he was reputed to have been executed for the publication of prohibited books in 1558. The production that actually led to so severe a sentence remained a riddle, however. The results of this research also show that nearly all the 'Van Oldenborch' publications which Dr Kronenberg regarded as post-incunabula appeared after 1540 and that a number of them can even be dated later than 1550. She placed the entire group notably too early. We can assume that this revision will be of consequence for the chronology of the Reformation in the Low Countries in so far as it depended on the diffusion of the new religious ideas in printed form.