The safety and efficacy of topical indigo naturalis in recalcitrant psoriasis was evaluated in a 12-week, randomized, observer-blind, vehicle-controlled study. Scaling, erythema, and induration scores improved significantly with the use of indigo naturalis ointment as compared to vehicle. Moreover, 74% of lesions responding to indigo naturalis had an excellent or near excellent clearance of psoriasis. Indigo naturalis was also well tolerated, since no serious adverse events were reported. The authors concluded that indigo naturalis was safe and effective in patients with plaque-type psoriasis and recommended that additional studies be conducted to determine its pharmacology (Yin-Ku Lin et al. Arch Dermatol 2008, 144[11]: 1457).