A double blind placebo controlled, 4-way crossover study was carried out to investigate the pharmacokinetics of single oral doses of xipamide (lOmg), triamterene (30mg) and Trirexan <10mg xipamide + 30mg triamterene) in a group of 12 healthy male volunteers. HPLC assays were developed for the measurement of both drugs in plasma. Plasma levels of xipamide and triamterene were measured using these validated HPLC methods. The individual plasma level data are presented as tables and the mean plasma levels are presented graphically. Plasma xipamide levels measured over a 24 hour period after dosing with xipamide alone and in a fixed combination as Trirexan were analysed using the JANA curve stripping program. The estimates of the pharmacokinetic parameters thus obtained were then used in curve fitting analysis using an IBM-PC compatible version of NONLIIT 84. Plasma triamterene levels after dosing with triamterene and Trirexan were likewise analysed.