1. Rhodium black and rhodium on charcoal catalyze the conversion of cycloolefins even at room temperature. In a mixture, cyclohexadiene-1, 3 reacts first, then cyclohexadiene-1, 4, and last the cyclohexene formed. 2. The direction of the conversions of cyclohexadiene isomers depends to different degrees on the hydrogen concentration on the surface of the catalyst. The hydrogenation of cyclohexadiene-1, 3 is accompanied by disproportionation at the usual hydrogen pressure, while that of cyclohexadiene-1,4 is accompanied by disproportionation only at reduced pressure. In an atmosphere of nitrogen, cyclohexadiene-1,3 disproportionates and is dehydrogenated. 3. Cyclohexene is hydrogenated more readily but dehydrogenated with greater difficulty than cyclohexadienes, and probably therefore does not disproportionate. 4. In the case when the cycloolefin cannot be dehydrogenated, disproportionation also is not observed.