In this study we evaluated the short-term oral antihypertensive effect of several peptide sequences isolated from casein fractions, previously characterized as in vitro angiotensin-converting enzyme-inhibitors, in spontaneously hypertensive rats (SHR). Systolic blood pressure (SBP) and the diastolic blood pressure (DBP) of the rats were measured by the tail cuff method before administration and also 2, 4, 6, 8 and 24 h post-administration. The sequences LVYPFTGPIPN, HLPLP, IAK, YAKPVA and WQVLPNAVPAK showed a clear decrease in SBP and DBP in SHR. HPHPHLSF caused a significant decrease of the DBP in the SHR, but this sequence did not modify the SBP of these animals in a significant manner. KKYNVPQL did not modify SBP in the SHR, and caused a slight, but significant and maintained, decrease in DBP in these animals. SBP and DBP returned to baseline values 24 h post-administration of all peptides. In conclusion, these peptides are bioactive ingredients with potential benefit in the prevention and treatment of hypertension or other associated disorders.