Most active antidandruff shampoos exhibit a strong activity against the yeast Malassezia ovalis. The present study was undertaken to compare the prolonged antifungal effect of three proprietary shampoos containing either 2% ketoconazole, 1.5% zinc pyrithione or 2.5% selenium sulphide. Superficial squames were harvested from the scalp in the days following a 6-week antifungal shampoo treatment. Counts of yeasts highlighted by a fluorochrome were made using computerized image analysis. Data show the increased duration of yeast reduction for the ketoconazole shampoo over the two other formulations. The lingering effect of ketoconazole is explained by the combination of its antifungal and pharmacokinetic properties.