Fungal infections (mycoses) are found throughout the world. Only a few structural classes of compounds currently satisfy the demands of modern chemotherapy in their treatment; hence, the quest for new types of active substances is of major scientific and therapeutic importance. The first representative of a new class of substances–the allylamine derivatives–namely naftifine ((E)-N-methyl-N-(1-naphthylmethyl)-3-phenylallylamine) was discovered by accident and has recently become commercially available as a topical antimycotic. The exploration of structure-activity relationships on the basis of naftifine and new synthetic strategies led to the discovery of the currently most active compound of this type, terbinafine, the first pharmaceutical agent to contain a (E)-1, 3-enyne structural element. Terbinafine exhibits considerably higher activity than the original “lead” structure naftifine both in vitro and in vivo; it is also up to one order of magnitude more effective than standard preparations in various chemotherapeutic animal tests after topical or oral administration. According to clinical experience gained so far, terbinafine is well tolerated and shows promising activity against various types of mycoses. Allylamines act as potent, selective inhibitors of fungal squalene epoxidase via a novel mechanism, which, unlike in the case of other inhibitors of steroid biosynthesis, does not depend on cytochrome P450.