Kozmin et al. contend that observations previously reported regarding the antimicrobial and antitumor activities of 6-N-hydroxy aminopurine (6-HAP) were incorrect. Their conclusions rely on poorly characterized reagents and focus strictly on in vitro techniques without validation in relevant mammalian model systems. We are pleased to be able to illuminate the weaknesses in their technical comment. The totality of current results continues to support our original conclusion that a strain of the common human commensal skin bacterium, Staphylococcus epidermidis, produces 6-HAP that can inhibit tumor growth. In their technical comment (1), the authors report that they used a commercially available form of 6-N-hydroxy aminopurine (6-HAP) purchased from MP Biomedicals (Chemical Abstracts Service no. 5667-20-9). We will refer to this chemical as 6-HAP-MPB. The authors used this reagent to test in vitro mutagenic activity. To investigate their discrepancies with our findings, we purchased 6-HAP-MPB from this supplier and observed that the reagent upon which they based their conclusions is not 6-HAP. That 6-HAP-MPB is not 6-N-hydroxy aminopurine is obvious from the package label that sta...