A quick and cost-effective technique of sample preparation followed by a reversed-phase high performance liquid chromatography under "organic solvent-free" (=100% aqueous) conditions for the simultaneous quantifying of sulfadimethoxine (SDM) and its metabolites, 6-hydroxy SDM (6-OH) and N(4)-acetyl SDM (N(4)-Ac), in chicken muscle is presented. Analysis by HPLC with photo-diode array detector was performed using a short C1 column with an isocratic 0.04 mol/l citric acid mobile phase. The method was validated by the analyses of spiked chicken muscle samples, resulting recoveries (> or =84%; relative standard deviations < or =6%), analytical total time (<1/2 h/sample, where a batch of 12 samples in 4 h), and limits of quantitation (< or =0.1 microg/g). The decision limits and detection capability were 0.019-0.106 and 0.054-0.112 microg/g, respectively. No organic solvents were used at all.