The fourth volume of Advances in Antiviral Drug Design is keeping up with the recent progress made in the broad field of antiviral drug research and encompasses six specific directions that have opened new avenues for the treatment of HIV and other virus infections.First, as the introductory chapter, the different new anti-HIV agents that are now in preclinical or clinical development are reviewed by E. De Clercq. This includes new NRTIs, NNRTIs and PIs, but also HIV entry/fusion inhibitors as well as integrase inhibitors, and some of these agents, such as the NRTI emtricitabine [(-)FTC] and the PI atazanavir, may soon be licensed for clinical use.Second, high expectations are vested in the potential therapeutic usefulness of inhibitors of HIV integration, a point of no return in the life cycle of HIV, and this approach is highlighted by D.J. Hazuda and S.D. Young.Third, as all currently available PIs can be described as "peptidomimetic", and, therefore, expected to demonstrate overlapping virus-drug resistance and side effect profiles, it would be interesting to see how a non-peptidic protease inhibitor such as tipranavir behaves, and this is covered by D. Mayers, K. Curry, V. Kohlbrenner and S. McCallister.Fourth, neuraminidase inhibitors such as zanamivir (that has to be inhaled) and oseltamivir (that can be administered via the oral route) have gained a definitive status as antiviral drugs useful for both therapy and prophylaxis of influenza A and B virus infections; as they target a specific influenza viral enzyme, neuraminidase (or sialidase),
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