The use of meconium to determine the exposure of a fetus to drugs of abuse is becoming a widely accepted protocol. However, the quantity of sample available for testing varies greatly between newborns and the material itself is complex in nature. Because of the small amount often collected, the sensitivity of analytical assay is extremely important. A confirmatory procedure for the determination of phencyclidine (PCP) in meconium using the selected ion storage (SIS) functions of an ion trap mass spectrometer is reported. The method is reproducible and detector response is linear over the range 0 to 250 ng/g. The limit of detection is 5 ng/g which provides a significant improvement in sensitivity over selected ion monitoring (SIM) mode electron impact quadropole analysis. The method is currently applied in our laboratory where the confirmation of PCP in meconium is a required analytical procedure. It is particularly useful for the analysis of meconium in which sample size is limited and sensitivity is an important factor.