Dr. Ertugrul’s letter confirms our primary claim that previous studies of this issue have employed mostly weak designs. The most informative control groups had characteristics demonstrably similar to those of the specified treatment groups in every respect except treatment assignment. As summarized by Dr. Ertugrul, previous studies have employed historical control groups (Meltzer and Okayli, 1995), control groups about which so little is known that comparability could not be assessed (Reid et al., 1998), and control groups that have included no patients who were not previously exposed to clozapine (Walker et al., 1997). Thus, we feel that Dr. Ertugrul’s comments provide substantial support for our evaluation of the literature.