ABSTRACT. This paper is devoted to the study of the problemWe assume that f can be written under the form /(t, u, u', u", u'") f2(t, u, u', u", u'")u" + fl (t, U, U', U", U"t)U' +fo(t, U, U', U", U"')U + r (t, u, u', u", u'") where r is a bounded fltnction. We obtain existence conditions related to uniqueness conditions for