The use of systemic antifungal therapy has significantly increased in recent years. Individualization of antifungal therapy through the use of serum or plasma concentrations has been suggested, although no specific recommendations have been developed. The important criteria for therapeutic drug monitoring and which of these criteria are satisfied by systemic antifungal agents are presented in this review. No one antifungal is ideally suited for application of therapeutic drug monitoring, but, under certain circumstances, obtaining serum or plasma concentrations can be justified. In patients who are susceptible to flucytosine toxicity, serum flucytosine concentrations should be monitored in an effort to avoid untoward side-effects. In contrast, therapeutic drug monitoring of amphotericin B is not recommended in the clinical setting. Demonstrating that ketoconazole and itraconazole are reaching the systemic circulation by obtaining serum concentrations may be clinically useful due to the large variability in their absorption and issues of patient compliance which may be seen with these agents. The bioavailability of fluconazole is much less varied although validation of compliance is a situation where obtaining serum concentrations may provide additional information.