We study the injective endomorphisms phi of the Baumsiag-Solitar group G(n,m) = [a,t\t(-1)a(n)t = a(m)] for n,m is an element of Z\{0} such that n,m not equal +/-1, and show that phi(a) is an element of boolean OR(i is an element of z)\{0}(a(i))(G). The proof is based on the Bass-Serre theory of graphs of groups.133525534