A sensitive and specific GC/MS method for the determination of methadone (MDN) and its two main metabolites, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) and 2-ethyl-5-methyl-3,3-diphenylpyrroline (EMDP), in plasma samples obtained from venous and arterial umbilical cord blood and maternal blood has been developed, optimized and validated. Specimen preparation includes protein precipitation with acetonitrile and simultaneous solid-phase extraction of the three analytes. Methadone-d9 was used as internal standard for the determination of MDN and EMDP, while EDDP-d3 for EDDP. Limits of detection were 0.6 microg/L for MDN and 0.3 microg/L for EDDP and EMDP, while limits of quantification were 2.0 microg/L for MDN and 1.0 microg/L for EDDP and EMDP. The calibration curves were linear up to 2000 microg/L for MDN and up to 1000 microg/L for EDDP and EMDP. Absolute recovery ranged from 94.8 to 99.7% for all three analytes. Intra- and interday accuracy was less than 5.3 and 5.5%, respectively, while intra- and interday precision was less than 3.5 and 5.0%, correspondingly, for all analytes. The method proved suitable for the determination of MDN and its two main metabolites in plasma samples obtained from umbilical cord and maternal blood of a woman participating in a MDN maintenance program, during the prenatal and postpartum period.