An extensive review with 51 refs. covering the TiX4/R3Al, TiX4/R2AlCl, TiCl4/R3Al2Cl3, and TiCl4/EtAlCl2 (X = Cl, Br; R = Et, i-Bu) systems as catalysts for cyclotrimerization of butadiene, the effects of temperature, pressure, Al:Ti mote ratio, and TiCl. concentration, the effect of butadiene impurities, water, and solvent type. The TiX4/R3Al system was found to be low active or inactive. With R3Al as reductor, activators like Ph3CCl, allyl chloride, benzyl chloride, and AlCl3 improved activity. TiCl4/Et3Al2Cl3 and TiCl4/Et2AlCl were most active (and selective) systems at 60-70 and 40-60degreesC, resp.