BACKING UP VEHICLE, PRESSED BRAKES, WENT TO FLOOR, NO BRAKES. PUT CAR IN NEUTRAL TILL VEHICLE STRUCK ANOTHER PARKED VEHICLE. PUT CAR IN DRIVE, PUT FOOT ON BRAKES TO STOP AND CHECK DAMAGE, NO BRAKES. PUT CAR IN NEUTRAL, CRUISED TO STOP. TRIED TO PUT CAR IN A PARKING SLOT, NO BRAKES, CAR PUT IN NEUTRAL AND I TURNED INTO A CURB TO STOP CAR. BEFORE LEAVING PUMPED BRAKE AND CHECKED FOR PRESSURE - NOW OK. DROVE HOME AND PARKED CAR IN DRIVE. CALLED GENERAL MOTORS TO HAVE CAR BRAKES CHECKED OUT. HAPPENED ONCE BEFORE - EXACT TIME UNKNOWN - IN PARKING LOT - WITH NO CARS AROUND, TO BACK INTO. NO PRESSURE ON BRAKE PEDAL. I THOUGHT I JUST MISSED THE BRAKE PEDAL. MINOR DAMAGE TO BOTH VEHICLES.