Among different lactic acid bacteria isolated from raw milk, 4 Enterococcus faecalis strains have stood out as producers of fermented milk with potent antihypertensive activity. The peptide beta-casein f(133-138), LHLPLP, was identified as one of the major peptides responsible for the activity of these fermented milk products. A simple method was developed to quantify this peptide in fermented milk using high-performance liquid chromatography coupled in line with mass spectrometry. This procedure does not require any previous sample fractionation or extraction, and direct analysis of the water-soluble extract obtained from the fermented milk can be performed. Validation studies showed sufficient specificity, reproducibility, linearity, and recovery, demonstrating that this method can be used for the routine quantification of LHLPLP during the production of fermented milk products. The developed method was readily applied to quantify the peptide LHLPLP under different fermentation conditions and with different aromatized products.