A film cooling investigation of the platform (endwall) between adjacent turbine blades is reported. The study concentrates on injection through a narrow slot, simulating the leakage of the coolant air through the seam between adjacent platforms. Nominal slot blowing rates of 0.06 and 0.12 are examined in the presence, and in the absence, of injection through a set of injection holes. Coolant to mainstream density ratio is 1.52. Reynolds number of the mainstream based on cord length and velocity upstream of the blade is about 120,000. Film cooling effectiveness is determined by measuring concentration of a tracer gas seeded in the coolant. The measured effectiveness values backed by visualization results give a useful picture of the film cooling due to the leakage. Injection through the slot, holes covered with tape, provides film cooling coverage for a region of endwall located between the slot and the blade suction side. Benefit from the slot injection is minimal on the upstream portion of the endwall. Higher slot blowing rate protects larger area and relocates regions of higher effectiveness. Covering the upstream half of the slot with tape improves downstream effectiveness slightly, but reduces the protected area. Results for the injection through the holes, with the slot taped, confirm findings of earlier reports. Combined slot and hole injections provide a very good coverage for the suction side portion of the endwall in the downstream half of the passage.