The disposition of deuterium-labelled cannabidiol, 2H2-CBD, was studied in five young men who were marihuana smokers. The pattern of use ranged from infrequent to frequent use of the drug. Plasma concentrations, determined by mass fragmentography, were followed for 72 h after both intravenous administration of 20 mg 2H2-CBD and smoking of an estimated amount of 18.8-19.4 mg 2H2-CBD. Systemic availability after smoking was determined by comparing the areas under the plasma concentration versus time curves for the two treatments and was found to be 31 +/- 13%. A four-fold difference in the availability of the compound was noted for the five subjects. Based on the area under the curve and the dose after intravenous administration, a plasma clearance of 960-1560 ml min-1 was calculated. A terminal elimination phase was not reached at 72 h, but the kinetic parameters were estimated from the 72 h beta-elimination. A half-life of 31 +/- 4 h after smoking and 24 +/- 6 h after injection was estimated as well as a distribution volume of 2520 +/- 470 l (32.7 +/- 8.61 kg-1).