The First Supplement adds to and updates the fourth edition of The International Pharmacopoeia. With publication of this Supplement the fourth edition of The International Pharmacopoeia now comprises the two main volumes published in 2006 and the first Supplement. This Supplement is published simultaneously in print and electronically by means of incorporation into a replacement CD-ROM (and on-line). This provides the user of The International Pharmacopoeia with a choice of form in which to consult the publication depending on the circumstances and the type of enquiry.New monographs: New monographs are included for: five antiretroviral substances; sixteen antiretroviral dosage forms including two fixed-dose combination preparations; one antimalarial dosage form; and six antituberculosis dosage forms including 2- 3- and 4-component fixed-dose preparations. Such specifications support the joint UNICEF-WHO-UN Prequalification project, managed by WHO. In developing these monographs WHO has worked closely with manufacturers, national authorities and national quality control laboratories. New general monographs for Liquid preparations for oral use and Oral powders are included to support the relevant specific dosage-form monographs. The monograph for Liquid preparations for oral use highlights that such preparations are often the dosage form of choice for paediatric use. This general monograph also includes a statement on Safety concerns in the section on Manufacture. This draws attention to the importance of ensuring the quality of starting materials. Failure to ensure that starting materials are of the required quality can have very serious consequences. Where a dosage form that is the subject of a new monograph in this Supplement is included in the first edition of the WHO Model List of Medicines for Children, an indication of the strength or strengths given in this new Model list is provided in the monograph. Such information is provided, where relevant, under the heading "Additional Information" following the statement concerning the strength(s) given in the main Model list. Revision: In parallel with the development of the new monograph for Doxycycline capsules, the published monographs for Doxycycline hyclate and Doxycycline tablets have been revised and replacement texts are included in this supplement. A requirement for dissolution has been included for several monographs. Infrared Reference spectra: Many monographs in The International Pharmacopoeia include an identification test using infrared spectroscopy; these tests usually allow comparison either with a spectrum obtained from the ICRS or with a reference spectrum. The majority of the infrared reference spectra are newly available and now published within this supplement.