18 Egyptian university graduates enrolled in TEOSL program, with approximately the same score on an objective test for their level, were presented with 8 variations of eight sentences (64 in all). Each sentence consists of two parts: the first part changes only in the adjective; and the second was negated by using (un-), (not), and (not un-) attached to the adjective. The purpose was to test the effect of negation on comprehension time. The results supported the hypotheses that negation delays comprehension in the second language; and (not) causes more difficulty in comprehension than the negative prefix (un-), even when (un-) is used to imply sentence negation and not only the adjective. The hypothesis that double negation causes more difficulty than single one, is also confirmed.