An experimental investigation of heat transfer to subcooled water under transient conditions has been conducted. Heat was generated electrically in platinum and aluminum ribbons in such a manner as to produce exponentially increasing heat generation rates which simulated reactor excursions. Surface temperature was measured, and the events were photographed with a high-speed camera. The temperature attained by the surface before boiling commenced and the time delay between passage of the boiling point and the beginning of boiling were measured. Heat flux at the beginning of film boiling was obtained. The effects of water temperature, exponential period, and gas concentration were studied. Periods ranged from 5 to 75 milliseconds. The bulk water temperature was varied from 90°F to near the boiling point; in all experiments the water was initially stagnant and at atmospheric pressure.