Profound and prolonged neutropenia following chemotherapy is a major risk factor for systemic fungal infections. It is still unclear how effective the various measures that are currently being used are in preventing serious fungal infection. Although a number of studies have been published on antifungal prophylaxis in neutropenic patients, there are a lot of conflicting data. At the present time, it seems that antifungal prophylaxis is more a matter of faith rather than science. The prophylactic use of fluconazole or itraconazole may reduce the incidence of systemic fungal infections in high-risk patient groups, mainly in patients with haematological malignancies. The antifungals currently used for prophylaxis in immunocompromised patients, and the toxicity of the antifungals are reviewed.