A fibroblast cell line was established from skin and lung tissue of the fruit bat (Rousettus aegyptiacus). 2. Genomic DNA, isolated from the fibroblast cells, was restriction digested and probed for the 9-kDa calbindin gene with a 180 base-pair fragment of mouse calbindin-D9K cDNA. Genomic DNA from rats and humans was similarly probed. 3. Hybridization and thus homology was observed between the mouse probe and DNA from the rat and the fruit bat, but not the human. 4. The results are discussed in relation to the detection of calbindin-D9K in the fruit bat despite very low circulating levels of its inducer 1,25(OH)2D3.