Endwall film cooling using curtain cooling and coolant discharge from upstream combustor walls is numerically examined in this study. Curtain cooling for the first-stage turbine vane endwall is accomplished by two rows of cylindrical film-cooling holes through the endwall at 20% of the axial chord length upstream of the vane leading edge. Flat plates with square trailing edges positioned upstream of the vane row model the combustor walls. Each is aligned with the leading edge of every second vane. A continuous slot is placed at the trailing edge of the combustor wall model through which the combustor wall coolant is discharged. Analyses of cases with various slot geometries document the effects on bonus cooling of the downstream endwall by the combustor coolant. Various endwall blowing ratios and slot-discharge flow ratios are applied. A comparison with a zero-slot-discharge datum case shows how the combustor wall discharge affects the flowfields near the passage endwalls. It is detrimental to endwall curtain cooling in some cases. Discharge effects on bonus cooling by combustor coolant are visible mainly near the vane leading edge and along the pressure side of the endwall passage.