We identified the proteins synthesized by Lactobacillus delbrueckii ssp. bulgaricus strain LBB.B5 in laboratory culture medium (MRS) at 37 �C and in milk at 37 and 4 �C. Cell-associated proteins were measured by gel-free, shotgun proteomics using high-performance liquid chromatography coupled with tandem mass spectrophotometry. A total of 635 proteins were recovered from all cultures, and among which 72 proteins were unique to or significantly more abundant in L. bulgaricus after growth in milk compared to MRS at 37 �C.