SWy-2 (Wyoming), STx-1 (Texas), and SAz-1 (Cheto, Arizona) montmorillonite and Sap-Ca saponite (California) were treated with different amounts of 12 M HCl and 1 M tetramethylammonium (TMA(+)) chloride solution at room temperature. The catalytic activity of these hybrid acid-activated organoclays (AAOCs) was directly measured using the isomerization of alpha-pinene at 120 degrees C for 1 h to yield camphene, limonene, and other minor products and compared to clays acid-treated in the absence of TMA(+) cations. The total conversion for the isomerization of cc-pinene was excellent for AAOCs formed from SWy-2 (88%) and STx-1 (73%), moderate for Sap-Ca (50%), and low for SAz-1 (20%). Samples treated with TMA(+) alone did not exhibit any marked catalytic activity. Acid-treated Sap-Ca and STx-1, which contained no TMA(+) cations were also effective catalysts for the isomerization process. TMA(+) cations were unexpectedly resistant to exchange by protons.