No / This study investigated and characterised transdermal permeation of bioactive agents from a topically applied Arnica montana tincture. Permeation experiments conducted over 48 h used polydimethylsiloxane (silastic) and human epidermal membranes mounted in Franz-type diffusion cells with a methanol-water (50:50 v/v) receptor fluid. A commercially available tincture of A. montana L. derived from dried Spanish flower heads was a donor solution. Further donor solutions prepared from this stock tincture concentrated the tincture constituents 1, 2 and 10 fold and its sesquiterpene lactones 10 fold. Permeants were assayed using a high-performance liquid chromatography method. Five components permeated through silastic membranes providing peaks with relative retention factors to an internal standard (santonin) of 0.28, 1.18, 1.45, 1.98 and 2.76, respectively. No permeant was detected within 12 h of applying the Arnica tincture onto human epidermal membranes. However, after 12 h, the first two of these components were detected. These were shown by Zimmermann reagent reaction to be sesquiterpene lactones and liquid chromatography/diode array detection/mass spectrometry indicated that these two permeants were 11,13-dihydrohelenalin (DH) analogues (methacrylate and tiglate esters). The same two components were also detected within 3 h of topical application of the 10-fold concentrated tincture and the concentrated sesquiterpene lactone extract.