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We used thin-layer chromatography of fecal bile acids in an attempt to separate feces of culpeo fox Pseudalopex culpaeus (Molina, 1782) from those of chilla fox P. griseus (Gray, 1837). We tested the method with pure bile acids and with feces from known fox species on two different plate types. Results differed according to the plate type used. The technique failed to distinguish scats from the two fox species. We found variability in the spot pattern of bile acids within species, and within individuals, likely associated to the diet. The location of the spots (Rf values) also varied with the concentration of the sample, and the color and location changed with different plate types. We warn that the thin-layer chromatography of fecal bile acids is sill unreliable for distinguishing feces between sympatric carnivores. Hence, we propose to rely on alternative techniques.