We demonstrate that both over-expression and suppression of the gene encoding the morphinan pathway enzyme salutaridinol 7- O -acetyltransferase (SalAT) in opium poppy affects the alkaloid products that accumulate. Over-expression of the gene in most of the transgenic events resulted in an increase in capsule morphine, codeine and hebaine on a dry-weight basis. The transgenic line with the highest alkaloid content had 41%, 37% and 42% greater total alkaloids than the control in three independent trials over 3 years. DNA-encoded hairpin RNA-mediated suppression of SalAT resulted in the novel accumulation of the alkaloid salutaridine at up to 23% of total alkaloid; this alkaloid is not detectable in the parental genotype. Salutaridine is not the substrate of SalAT but the substrate of the previous enzyme in the pathway, salutaridine reductase. RNA transcript analysis of 16 primary T 0 transformants and their segregating T 1 progeny revealed an average reduction in SalAT transcript to about 2% of the control. Reduction in SalAT transcript was evident in both leaves and latex. Reverse transcriptase PCR and highperformance liquid chromatography analyses confirmed cosegregation of the expressed transgene with the salutaridine accumulating phenotype.