On July 14, 1997, at 2034 hours Pacific daylight time, the flight crew on United Airlines Flight 2327, reported an exposure to a laser beam during an approach to Ontario, California. The aircraft, a Boeing 737-522, N956UA, was operated by United Airlines as a regularly scheduled domestic passenger flight under 14 CFR Part 121 when the incident occurred. The flight originated in San Francisco, California, at 1938 on the evening of the incident. Visual meteorological conditions prevailed at the assigned altitude and an IFR flight plan was filed. The aircraft was descending through 4,000 feet msl on a vector to intercept the final approach course to runway 26R at Ontario when the crew noticed a red laser beam that swept across the cockpit five to six times. About 5 seconds later, the laser encounter reoccurred. The aircraft was between 4 and 5 miles from the approach end of the runway when the crew saw the laser emanating from a point on the ground about 1.5 miles north of their position. The crew notified air traffic control of the incident. There were no reports of injury to anyone onboard the aircraft. Investigators from the FDA, the FBI, and the San Bernardino County Sheriff's Aero Bureau were notified; however, the source of the light remains undetermined. According to the FAA, there were no NOTAMs in effect for laser light activity in the Ontario area at the time of the incident.