In 160 000 hadronic Z decays recorded with the ALEPH detector at LEP, the yields of Λℓ− and Λℓ+ combinations have been measured. The observed excess of Λℓ− over Λℓ+ of 53±13 is interpreted as evidence for b baryons and their semileptonic decay. Assuming that three body decay processes such as dominate the semileptonic decay of b baryons, this ex cess corresponds to a product branching ratio , where ΛbandΛc+ denote the bottom and charm baryons respectively.