In the limestone quarries in the southern part of the province of Limburg, Netherlands, 13 species of Isopoda Oniscoidea were found during an intensive exploration (1946-1958) of the obscuricole fauna of these artificial caves. None of the species found is troglobiont, all have to be classed as troglophile or trogloxene, as all are to be met with also outside the caves. Four of the species (Platyarthrus hoffmannseggii, Philoscia muscorum, Trachelipus rathkii and Porcellio spinicornis) probably have to be ranged among the trogloxene, as all four were found only once, and then either near the cave entrance or at a place where the roof of the cave had collapsed and epigaean debris fallen in. All 13 species (with the possible exception of Porcellio laevis) form part of the outside fauna of the area. The relative frequency of the species inside and outside the caves, however, is not the same. Porcellio laevis has thus far been found with certainty only inside the caves. P. dilatatus and Armadillidium pictum, when compared to the other species, are clearly more frequent inside the caves than out. Porcellio scaber and Oniscus asellus are the most common terrestrial isopods both inside and outside the caves, but although Oniscus asellus in the caves has been found about twice as often as Porcellio scaber, and in about twice as large numbers, it is my strong impression that outside it is Porcellio scaber which is the more frequent. Armadillidium vulgare which outside is the third commonest species trails very far behind inside the caves, being even far less frequent than A. pictum.