Optimum conditions for the direct reversed-phase LC determination of fluoride based on the ternary M-(F-)-(5-Br-PADAP) complexes [M = ZrIV or HfIV and 5-Br-PADAP = 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol] were evaluated. Chromatographic separation was performed with C18 end-capped column with an eluent consisting of acetonitrile-water (85 + 15 v/v) mixture of pH 4.0 +/- 0.3 (flow rate 1 ml min-1), and the eluate was monitored spectrophotometrically at lambda max = 585 nm. The calibration curves were linear over a wide range of fluoride concentrations: from 1 to 110 and 150 ng ml-1 for the ZrIV-(F-)-(5-Br-PADAP) and HfIV-(F-)-(5-Br-PADAP) systems, respectively (using a 20 microliters loop). Under such conditions the detection limits were 0.8 and 0.7 ng ml-1, respectively, and the quantification limit is 1.0 ng ml-1 for both methods. When a 100 microliters loop was used, the limits of both detection and quantification in the method based on the zirconium system were 0.2 ng ml-1. Using the proposed method, fluoride was determined directly in tap water, saliva and an anti-cancer agent for prostatic cancer (Leuprolid).