The object of this study was to correlate blood morphine concentrations to regional brain concentrations and indirectly to opiate receptor density. Brain sections obtained postmortem from 21 suspected heroin-associated fatalities were analyzed for morphine by gas chromatography with FID. In all of the cases where death was attributed to narcotic overdose the concentration of morphine was found to exceed the minimum fatal concentration, 0.2 microgram/g of tissue, in one or more of the brain sections, whereas the blood concentration exceeded 0.2 microgram/g in only five cases. The correlation between the concentrations in the thalamus and blood were very good, suggesting that the thalamus could be used to estimate blood morphine concentration by the forensic toxicologist. Statistical analysis of the data is presented.