The study found hydromorphone at a concentration greater than 5 ng/ml in 36 of the 73 urine specimens. Hydromorphone concentrations ranged from 0.02 percent to 12 percent of the morphine concentration. Hydrocodone was not detected in these specimens at the assay detection limit of 25 ng/ml. These findings support earlier work that suggests the detection of hydromorphone in urine specimens does not necessarily mean that exogenous hydromorphone or hydrocodone was used by the subject being tested; however, when small amounts of hydromorphone are present in urine, elevated concentrations of morphine should also be present. Another explanation for small concentrations of hydromorphone other than the effect of metabolism on morphine is that hydromorphone is a contaminant of the illicit drugs consumed; for example, codeine was found in 64 percent of the urine specimens. Acetylcodeine is a known contaminant in heroin, and the body converts acetylcodeine to codeine in an analogous process to the deacetylation of heroin to 6-acetyl-morphine and then to morphine. The opioids were analyzed by gas chromatography-mass spectrometry as their respective trimethylsilyl derivatives following solid phase extraction. The limit of detection for hydromorphone was 5 ng/ml. 2 tables and 4 references