A method is described for the determination of nefazodone and its active metabolites hydroxynefazodone, the dione BMS-180492 and m-chlorophenylpiperazine in blood plasma and expressed human milk based on reversed-phase high-performance liquid chromatography. Measurements were performed on drug-free plasma and expressed human milk spiked with nefazodone and metabolites to prepare and validate standard curves and specimens collected from nursing mothers. Parent drug and metabolites were separated from the biological matrices by solid-phase extraction using CERTIFY columns. Chromatographic separation was achieved with a C18 column and compounds were detected by their absorbance at 205 nm. Trazodone was used as an internal standard. The assay was validated for each analyte in the concentration range 200 to 1200 ng/ml.