Error tolerance is an important subject which has far reaching implications for the teaching of foreign languages. If certain errors can be tolerated and others cannot, then the teacher has to have at his disposal a scale showing the gravity of the errors, which would function as a guide to the evaluation of the written as well as the spoken performance of his students. Appeal is made to the judgement of native speakers of English on the gravity of syntactic errors through a questionnaire distributed to sixty British English judges of different ages, sexes and professions. The results obtained clearly show that global errors involving multiple deviations, wrong word order, nd wrong verb forms are considered more serious and therefore less tolerable than local errors involving the negative and interrogative formation, use of articles and parts of speech. Native speakers' judgements as to error gravity and therefore error tolerance seemns to be proportionally related to intelligibility; the more, intelligible the utterance, the more tolerable the error. However, error tolerance seems to be affected by other variables including the sex, age and profession of the judge.