The bonding techniques employed in orthodontic practice differ from those used in restorative dentistry for, upon the completion of treatment, the appliance is removed. This necessitates breaking the resin/enamel bond. Ideally a smooth, undamaged enamel surface free from all traces of bonding agent should result. Regrettably, however, this ideal is rarely achieved. This investigation assessed the effects of a commercial debonding agent (P-de-A, Oradent Ltd, Eton, Berks, UK), derived from peppermint oil, upon the surface microhardness of two orthodontic resins (Orthodontic Concise and Transbond, both 3M, St Paul, MN, USA). Twenty discs (10 mm diameter × 1.25 mm deep) of each resin were fabricated and, following 1 week's storage in distilled water at 37 °C, were allocated to application groups composed of four specimens. The mean initial surface hardness of each group was then determined prior to the application of P-de-A for one of: 30, 60, 90, 120 and 180 s. The hardness was then remeasured. One-way analyses of variance were performed upon the mean initial and final hardness data and revealed only a significant (P < 0.05) reduction in surface hardness following the 180 s application of P-de-A to Orthodontic Concise. We were therefore unable to find little evidence to suggest that the agent facilitates debonding by a softening mechanism and further work is required to elucidate the means whereby orthodontic debonding and 'clean-up' of residual composite, as reported by others, is facilitated.