We measured morphine and codeine in commercially available poppy seeds and in serum and urine samples from healthy adults who had ingested these poppy seeds. Four brands of black poppy seeds, examined by gas chromatography-mass spectroscopy (GC-MS) with deuterated internal standards, contained from 17 to 294 micrograms of morphine and 3 to 14 micrograms of codeine per gram of seeds. Morphine was detected by GC-MS in hydrolysates of serum as late as 24 h after ingestion, with a maximum mean concentration of 100 ng/mL (range 82-131) measured 2 h after the subjects ingested 25 g of seeds. Opiates were detectable (greater than 300 micrograms/L) in urine by enzyme-multiplied immunoassay (EMIT; Syva Co.) and by radioimmunoassay screening procedures for as long as 48 h after ingestion. The identity and quantities of morphine and codeine in poppy seed extracts and in hydrolysates of serum and urine were confirmed by GC-MS. Therefore a positive finding of morphine or codeine in blood and urine may sometimes be due to ingestion of poppy seeds.