A study examined student abilities to integrate semantically related propositions; and identified sources of comprehension difficulty for the unskilled reader. It also examined the influence of two types of relations (causal and adversative) and two types of connectives (conjunctions and verbs) on readers' comprehension, on-line integration of related propositions, and contextual influences. Subjects, 32 high school students of varying reading ability levels, read 96 passages, classifying each as either semantically consistent or anomalous. Results of analysis showed that comprehension and on-line integration of semantic relations were influenced by contextual constraints, by readers' skill in using such constraints, and by type of relation. Adversative relations proved more difficult than causal ones, though comprehension seemed directly related to reader skill. Skilled readers were unaffected by connective type, whereas less skilled readers' comprehension seemed to depend upon the marking of a relation by a conjunction. Skilled readers were equally accurate in comprehending consistent and anomalous passages, while less skilled readers were highly inaccurate in judging anomalous passages, even though they took more time to read those passages. (Tables of data are included.) (Author/JD)