One Sense Per Discourse 
 
 It is well-known that there are polysemous words like sentence whose meaning or sense depends on the context of use. We have recently reported on two new word-sense disambiguation systems , one trained on bilingual material (the Canadian Hansards ) and the other trained on monolingual material ( Roget's Thesaurus and Grolier's Encyclopedia ). As this work was nearing completion, we observed a very strong discourse effect. That is, if a polysemous word such as sentence appears two or more times in a well-written discourse , it is extremely likely that they will all share the same sense . This paper describes an experiment which confirmed this hypothesis and found that the tendency to share sense in the same discourse is extremely strong (98%). This result can be used as an additional source of constraint for improving the performance of the word-sense disambiguation algorithm . In addition, it could also be used to help evaluate disambiguation algorithms that did not make use of the discourse constraint .  