We appreciate this additional information concerning the need for close patient monitoring when patients taking dapsone for Pneumocystis carinii pneumonia (PCP) prophylaxis or treatment receive concomitant rifampin therapy. Certainly, sensitivity differences between P carinii and Mycobacterium leprae as well as potentially lower dapsone dosages used for PCP prophylaxis are important differences between leprosy treatment and PCP prophylaxis. As we noted in Table 2 of the rifampin drug interactions update,1 human studies of this interaction in patients with PCP are needed to further establish its importance. In addition, these studies should certainly include patients taking dapsone for PCP prophylaxis who receive concomitant rifampin therapy. Additional studies in leprosy patients are needed as well.