UFOS AND THE EXTRATERRESTRIAL CONTACT MOVEMENT: A BIBLIOGRAPHY/VOL ONE & UNIDENTIFIED FLYING OBJECTS/VOL TWO : THE EXTRATERRESTRIAL CONTACT MOVEMENT BY GEORGE M. EBERHART (1986)
UFOS AND RELATED SUBJECTS: AN ANNOTATED BIBLIOGRAPHY BY LYNN E. CATOE, LIBRARY OF CONGRESS, DEFENSE TECHNICAL INFORMATION CENTER (1969)
SUBTERRANEAN WORLDS: 100,000 YEARS OF DRAGONS, DWARFS, THE DEAD, LOST RACES AND UFOS FROM INSIDE THE EARTH BY WALTER KAFTON-MINKEL (1989)