THE RELATIONSHIPS BETWEEN READER EFFICIENCY IN PROCESSING SENTENCES AND DIFFERENCES IN THE DEEP STRUCTURE OF THE STIMULUS SENTENCES WERE STUDIED. THE EFFICIENCY OF PROCESSING, AS MEASURED BY THE SUBJECTS' EYE-VOICE SPAN, VARIED WITH CHANGES IN THE DEEP STRUCTURE. COMPARISONS WERE MADE BETWEEN READER PROCESSING OF PAIRS OF SENTENCES IN WHICH THE SURFACE STRUCTURE WAS THE SAME, BUT IN WHICH THE DEEP STRUCTURE WAS DIFFERENT. THE EYE-VOICE SPAN MEASURE VALIDLY DISCRIMINATED BETWEEN SENTENCES WITH THE SAME SURFACE STRUCTURE BUT WITH DIFFERING DEEP STRUCTURE. THE RESULTS WERE INTERPRETED TO SUGGEST VERY TENTATIVELY THAT THE EFFICIENCY OF READING PROCESSING IS (1) A FUNCTION OF THE "CONGRUENCE" OR "CONSTRAINTS" BETWEEN THE SURFACE STRUCTURE AND THE DEEP STRUCTURE OF SENTENCES, AND ALSO (2) A FUNCTION OF THE NUMBER OF STRUCTURAL "CATEGORIES" REQUIRED IN THE DEEP STRUCTURE. (AUTHOR/MC)