The clinical outcome and the effects on morphogenesis and cell ultrastructure induced by a 1% ciclopiroxolamine solution in six patients with proven pityriasis versicolor were studied. Treatment regimens consisting of a once-daily application for 1 day, 2 days (Days 1 and 4) or 3 days (Days 1, 4 and 8). Clinical evaluation, scanning (SEM) and transmission electron microscopy (TEM) were performed on skin scrapings before treatment, and at 3, 7, 15 and 21 days after the start of therapy. SEM techniques have shown severe changes in the surface ultrastructure of yeasts and hyphae of Pityrosporum spp. (Malassezia furfur) 15 days after the start of therapy. TEM techniques showed extensive internal disruption, mainly severe necrosis of the cytoplasm, 3 and 7 days after the start of treatment. However, KOH direct microscopy showed apparently normal morphology of Pityrosporum spp. (Malassezia furfur) at all assessment points. The final clinical cure in all the patients was achieved 21 days after the start of therapy.