Metathesis of perdeuterio- and perhydroethene, propene, 1-butene, and their mixtures with cis-2-butene was studied over a molybdena-alumina catalyst using recirculation and pulse systems. No metathesis was observed over a fresh unreduced catalyst, but after pretreatment with cis-2-butene the reactivity of olefins in metathesis reactions increased in the sequence of ethene ⪡ 1-butene < propene < cis-2-butene. The activity was higher for the metathesis of propene or 1-butene after the catalyst was pretreated with the corresponding olefin instead of cis-2-butene, but no metathesis was induced by ethene. Metathesis of cis-2-butene was suppressed by the addition of equal amounts of olefins in the sequence: ethene ⪡ 1-butene < propene. Studies of mixtures revealed that the rate of cis- to trans-2-butene isomerization by metathesis ∼- the rate of degenerate metathesis of 1-butene or the cross metathesis of 1-butene with 2-butene.