Abstract.Let R be a ring and f an endomorphism obtained from sums and compositions of left multiplications, right multiplications, automorphisms, and derivations. We prove several results relating the behavior of / on certain subsets of R to its behavior on all of R . For example, we prove ( 1 ) if R is prime with ideal / / 0 such that /(/) = 0, then f(R) = 0, (2) if R is a domain with right ideal X ¿ 0 such that f(X) = 0, then f(R) = 0, and (3) if R is prime and /(A") = 0 , for X a right ideal and n > 1 , then f(X) = 0 . We also prove some generalizations of these results for semiprime rings and rings with no non-zero nilpotent elements.