Δ9-Tetrahydrocannabinol, as monitored by flame-ionization GLC at various temperatures, degrades by a biphasic semilogarithmic curve with time in acidic aqueous solutions (<1 mg/ liter) below pH 4 to GLC-observable products with separate retention times and the degradations are specific hydrogen-ion catalyzed. The products are considered as Δ8-tetrahydrocannabinol, P1, P2, and P3 and can be observed and isolated by TLC. These products do not appear above pH 4 in the neutral region, and these degradations are primarily first order, are not biphasic, and are pH independent. The half-life of Δ9-tetrahydrocannabinol is about 15 min at 37° and pH 1, typical stomach conditions. The product P1 may give rise to cannabinol by the GLC and TLC procedures since the IR, UV, TLC, NMR, and GLC of thin-layer chromatographed P1 and cannabinol are coincident, but chloroform extracts do not show the higher absorbances expected if the product that forms in solution to give P1 is cannabinol. The products P2 and P3, isolated by TLC, are consistent with the expected properties of Δ9-hydroxycannabidiol and 9-hydroxycannabinol, respectively, by IR, UV, NMR, and mass spectroscopy. The final amounts of Δ8-tetrahydrocannabinol, P1, P2, and P3 are in a constant ratio independent of pH below pH 4. Δ9-Tetrahydrocannabinol, as monitored by flame-ionization GLC, degrades solely by a first-order process to an equilibrium with P2 and Pa at acidic pH values and the process is specific hydrogen-ion catalyzed. The equilibrium appears to be independent of pH below pH 4 and is the same when TLC-isolated P2 or P3 is used as the starting material. It follows that the acidcatalyzed isolated double-bond migration favors Δ8-tetrahydrocannabinol over the Δ9 compound, and it is most probable that the equilibrating P2 and P3 are results of water addition to the isolated double bond and ether solvolysis. The product that gives rise to the P1 retention time that ultimately gives cannabinol is structurally indeterminate at present.