Electronic Journal of Differential Equations, Vol. 2000(2000), No. 56, pp. 1-18. Title: Uniqueness of rapidly oscillating periodic solutions to a singularly perturbed differential-delay equation Author: Hari P. Krishnan (Chicago, IL, USA) Abstract: In this paper, we prove a uniqueness theorem for rapidly oscillating periodic solutions of the singularly perturbed differential-delay equation $\varepsilon \dot{x}(t)=-x(t)+f(x(t-1))$. In particular, we show that, for a given oscillation rate, there exists exactly one periodic solution to the above equation. Our proof relies upon a generalization of Lin's method, and is valid under generic conditions. Submitted December 1, 1999. Published July 24, 2000. Math Subject Classifications: 34K26, 37G10. Key Words: delay equation; rapidly oscillating; singularly perturbed.