Diuretics are therapeutic agents used to promote the excretion of bodily fluids and salts. They are also misused by some athletes to decrease body mass or to mask the use of anabolic steroids and other drugs. We have developed a method that screens for diuretics in urine and blood serum. Two successive runs were required because of the heterogeneity of this group of compounds. Screening for diuretics that contained sulphonamide and/or carboxylic groups was done at pH 10.6 with 3-(cyclohexylamino)-1-propane-sulphonic acid (0.06 M) as buffer. Diuretics that contained primary, secondary or tertiary amine groups were investigated at pH 4.5 with an acetate (0.07 M)-betaine (0.5 M) buffer system. Hydrostatic injection mode for 5 s gave the best efficiency. Longer injection times were acceptable but efficiency was then somewhat reduced. Detection limits at the low femtomole level are achievable for most compounds with a UV-Vis detector operating at 220 and 215 nm. Temperature affected the separation, and 20 degrees C proved best. All compounds were separated in less than 30 mins. A confirmation analysis of all compounds was done by GC-MS.