Résumé : Twenty examples of π+ mesonic decays of light hypernuclei have been found together with 7000 π- mesonic decays. The ratio R4 of π+ mesonic decays for the gL4 He hypernucleus has been computed from the results of this work and those of a previous experiment [1] and is found to lie between the values 5.4 ± 1.5%1.7% and 6.9 ± 1.8%2.1%. The π+ mesonic decays of other species of hypernuclei are briefly discussed. © 1969.