IN THE DEVELOPMENT OF A PROGRAM FOR MECHANIZING TRANSLATION, SOME PROBLEMS WOULD REMAIN EVEN WHEN THE MORPHEMES AND GRAMMATICAL PROCESSES INVOLVED ARE REASONABLY EQUIVALENT IN THE TWO LANGUAGES. EQUIVALENT GRAMMATICAL RELATION HAS TO BE DEFINED BECAUSE IMPORTANT STRUCTURAL SIMILARITIES AMONG SENTENCES ARE FOUND MORE OFTEN IN THEIR DEEP STRUCTURE THAN IN THEIR SURFACE STRUCTURE. THUS, TWO SENTENCES ARE EQUIVALENT IF (1) THE UNDERLYING SIMPLE SENTENCES ARE TRANSLATIONS OF EACH OTHER, (2) THE RELATIONS BETWEEN THESE UNDERLYING SENTENCES AND A PORTION OF THE RESULTING SENTENCE ARE EQUIVALENT, AND (3) THE RESULTING SENTENCES ARE TRANSLATIONS OF EACH OTHER. HOWEVER, STRICT EQUIVALENCE AMONG GRAMMATICAL RELATIONS IS NOT TO BE FOUND. DISPARITIES IN SENTENCE STRUCTURE ARE ILLUSTRATED WITH SENTENCES FROM CHINESE, JAPANESE, AND ENGLISH, AND DEEP-SEATED SYSTEMATIC DIFFERENCES ARE FOUND. (IT)