Let R be a prime ring of
characteristic ≠2 with a derivation d≠0 and a non-central Lie ideal U such
that d(u)n is central, for all u ∈ U. We prove that R must satisfy s4, the
standard identity in 4 variables; hence R is either commutative or an order in a
4-dimensional simple algebra. This result extends a theorem of Herstein to Lie
ideals.