Platinum-alumina catalysts were prepared at 20 degrees C by using a method in which hexachloroplatinic anions from solution were adsorbed on theta-alumina in the pH range 1-10 and with contact times between 1 and 24 h. An adsorption maximum was observed at pH around 3-4. From measurements of electrophoretic mobility, the isoelectric point of theta-alumina was determined to be about 8.5. Comparison with literature data indicated that gamma- and theta-alumina exhibit similar adsorption properties and that the amount of Pt deposited is controlled by pH and contact time for both systems. The adsorption appears to proceed initially as a physisorption process with relatively strong specific interaction or chemisorption taking over at longer contact times. Pt/theta-alumina samples with 0.3 to 2.2 wt% Pt were prepared. Wet calcination at 570 degrees C led to a decrease in the Cl content of the samples, while the Pt content was unaffected.