Blood and urine may contain the analytes morphine and codeine as a result of the legal ingestion of certain drug products, poppy seeds, or products containing poppy seeds. The small amount of morphine (usually less than 200 ug/g seeds) and codeine is enough to produce a positive urinalysis for opiates. Current data on the levels of morphine and codeine in poppy seed products and in the resulting urine specimens from individuals consuming these products are reviewed. The metabolism and elimination of these drugs are discussed and guidelines for differentiating poppy seed ingestion from codeine, morphine, or heroin abuse are offered. 2 tables, 29 references. (Author abstract modified)