This study investigated the effects of the probiotic Lactobacillus acidophilus strain DSM 13241 in dogs with non-specific dietary sensitivity (NSS). Six adult German Shorthair Pointers with NSS consecutively received a control dry diet and the same diet supplemented with the probiotic (6 x 10(6) cfu/g) for 12 weeks each, followed by another control period of four weeks. Frequency of defecations, faecal quality and nutrient digestibility were determined. Faeces were cultured for Clostridium perfringens, Escherichia spp., lactobacilli and bifidobacteria and quantitative fluorescence in situ hybridisation (FISH) was performed. Feeding the probiotic improved faecal consistency, faecal dry matter and defecation frequency (p < 0.05). Faecal concentrations of culturable lactobacilli and bifidobacteria increased numerically, but not significantly, also the decrease of the numbers of C. perfringens and Escherichia spp. did not reach the level of significance. Results from FISH showed more constant bacterial populations. It can be concluded that L. acidophilus DSM 13241 can stabilise the digestive processes in dogs with NSS.