Work has been carried out on a number of structural problems related to proteins derived from retroviruses and of relevance to the pathogenesis and clinical manifestation of AIDS. These include the potent anti HIV protein cyanovirin-N, variants thereof and HIV-1 protease, in particular a monomeric form of this enzyme. In addition, methodological advances have been made in devising new pulse sequences to easily measure residual dipolar couplings of aligned biological macromolecules in the magnetic field.