As is well-known, the Rost invariant describes the degree 3 cohomological invariants of a semisimple simply connected group. In a recent preprint, A. Merkurjev has extended this result by producing an exact sequence which includes as one of the terms the group of degree 3 normalized cohomological invariants of a semisimple algebraic group G. He then uses this sequence to describe the invariants for all adjoint groups of inner type. We use his sequence to study the degree 3 invariants of split groups of types A and D that are neither simply connected nor adjoint. As a consequence, we recover relations to many of the known results and find new invariants that have not been previously described in the literature. (Joint work with H. Bermudez)