Replacement of one triazole ring of fluconazole with 4-pyridinyl leads to an increase in activity against Aspergillusfumigatus. Introduction of an t~-methyl group has a marked additional beneficial effect. Investigation of pyridinyl and pyrimidinyl analogues resulted in the identification of 30 (UK-109,496, voriconazole) which has excellent potency against a broad range of fungal pathogens including A. fumigatus and Candida krusei.