The authors consider a higher order nonlinear neutral differential equation of the form
where is even, is a constant; , ; is not identically zero on any ray , ; , and ; is nondecreasing in each of the variables.
In Theorem 1, there are established conditions under which every proper solution of (1) is oscillatory. This result is reformulated as Theorem 2 for the special case, where
, for . The result of Theorem 1 is illustrated by an example.