An understanding of the mechanisms of action and in vitro profiles of antifungal agents is pivotal to selecting effective treatments for dermatophytoses. The principal mechanisms of action of antifungal drugs include disruption of spindle and cytoplasmic microtubule function (e.g., griseofulvin), depletion of or binding to ergosterol (e.g., terbinafine, ketoconazole, and amphotericin B), and accumulation of squalene (terbinafine). It is likely that antifungal agents that deplete or bind to ergosterol have fungistatic activity only; agents that produce a concomitant accumulation of intracellular squalene have fungicidal activity. Although the mechanism of action markedly influences the clinical efficacy of an antifungal agent, in vitro and in vivo antimycotic profiles and bioavailability factors such as drug access to the stratum corneum also contribute to the effectiveness of antifungal agents. © 1993, American Academy of Dermatology, Inc.. All rights reserved.