X-ray crystallographic, energy minimization and quantum mechanical calculations are being employed on compounds of biological interest to give insights into and explanation of their modes of behavior. Various compounds showing promise against the AIDS virus or cancer are being systematically investigated to obtain structural and electronic properties which may help elucidate the mechanism of their action and thus lead to improved analogs. The x-ray structures of temozolomide and geldanamycin are being determined. Strain energies and quantum calculations are being carried out on these compounds.