Isotretinoin is a retinoid that is converted in vivo into all-trans retinoic acid and has diverse biological activities.^1,2,3,4 It increases the doubling time and transcription of retinoic acid receptor β (RARβ) mRNA in Hep2, FaDu, CCL-17, SCC-9, SCC-15, and SCC-25 human oral squamous cell carcinoma cells when used at a concentration of 1 μM.² Isotretinoin inhibits proliferation of primary human sebocytes (IC50 = 10 μM).³ It also decreases triglyceride, stearyl ester, and free fatty acid synthesis and modulates keratin expression in primary human sebocytes at a concentration of 0.1 μM. Isotretinoin (2 mg/kg per day) reduces chronic rejection damage and decreases mRNA expression of IFN-γ and IL-10 in allografts in chronic Fisher344➛Lewis transplant mice, an allograft nephropathy model.⁴ It also slows rod and cone recovery and prevents light-induced photoreceptor damage in an albino rat model of photoreceptor degeneration when administered at a dose of 40 mg/kg.⁵ Formulations containing isotretinoin have been used in the treatment of severe recalcitrant nodular acne.