Transmission of abused drugs to infants through drug use during pregnancy is being monitored in a state program that obtains meconium from newborns in hospitals selected to represent the various strata among the whole population. Unexpectedly high rates of positive results for tetrahydrocannabinoids has necessitated further analysis of the reserved remainder of thepreviously examined meconium samples to determine whether the standard method (FPIA) gives false positives. A mass spectrometric method was devised, similar to a published method, butmodified to handle stored samples. The mass spectrometric method indicated a lower overall rate. Results obtained have been verified by a commercial laboratory that specializes in this type of assay and further recently collected samples have been submitted for analysis.