Abstract: Direct Viable Count (DVC) method has been recently combined with fluorescent in situ hybridization (FISH) for the specific detection of viable cells of Lactobacillus delbrueckii subsp. bulgaricus CECT 4005T and Streptococcus thermophilus CECT 801. This method has been used to determine their in vitro viability to gastrointestinal juices, being the resistance of L. delbrueckii subsp. bulgaricus and S. thermophilus 26.2% and 9.2%, respectively. On the other hand, an in vivo study has been carried out with the application of this technique for their detection in human feces, after consuming fermented milk. Cells of L. delbrueckii subsp. bulgaricus CECT 4005T were not detected, whereas viable cells of S. thermophilus CECT 801 were detected in a number higher than 103 cells per gram in a 30% of the samples after 4 wk of consumption. DVC-FISH is a quick and culture-independent useful method, which has been applied for the 1st time in an in vivo survival study of LAB.