The animals used for the pharmacological study reported in JMRI in 2004 (1) were all from the same study and therefore had been immunized with the same batch of guinea pig myelin and adjuvant. We were completely aware of the variability associated with the immunization procedure applied. 1. The results from the control group were reported in the MRM paper of 2003 (2), the aims of which were to describe the validation of the approach of using USPIOs to monitor macrophage infiltration in this EAE model, and to demonstrate the mismatch between Gd-DOTA uptake and USPIO distribution. Thus the MRM 2003 paper focused on methodological aspects and included only control (no drug-treated) animals. We think it is a good scientific procedure to expose the method validation to the critical views of peer reviewers before describing pharmacological applications. 2. The JMRI paper presented the pharmacological application of the technique described. Substantially more data were included in this second article, while obviously the data from the control group remained the same. The focus of the JMRI article was to demonstrate the effect of acute and chronic drug intervention on EAE, and thus was clearly different from that of the MRM article. A minor aspect: Because of confidentiality issues, we were able to report the data on drug-treated animals only recently. 3. The MRM 2003 article is referred to in the JMRI paper (Ref. 16), but admittedly not in the corresponding figure legend. In summary, both the vehicle- and drug-treated groups were immunized with the same batch, which allows us to draw conclusions concerning the therapy response to that particular drug intervention. With kind regards, Martin Rausch [email protected]*, Markus Rudin*, * Novartis Pharma AG, Analytical and Imaging Sciences, Basel, Switzerland.