Serum levels of glyceryl trinitrate have been determined in eight healthy subjects following transdermal application of four different glyceryl trinitrate plasters using a randomised crossover design. The plasters investigated were Deponit 10, Nitradisc 10, Nitroderm TTS 10 and Nitro-Pflaster-ratiopharm 10. The medians of serum concentrations arranged in decreasing order were 0.17-0.23 ng/ml for Nitroderm TTS 10, 0.13-0.21 ng/ml for Nitradisc 10, 0.08-0.13 ng/ml for Deponit 10, and 0.04-0.09 ng/ml for Nitro-Pflaster-ratiopharm 10. Corresponding areas under the concentration-time curves (AUC 0-24) were 23.15 nmol . h/l (Nitroderm TTS), 20.32 nmol . h/l (Nitradisc), 10.39 nmol . h/l (Deponit), and 5.7 nmol . h/l (Nitro-Pflaster-ratiopharm).