  By employing recent data on non-mesonic decay of s-shell Lambda-hypernuclei
we study, within the phenomenological model of Block and Dalitz, the validity
of the Delta I=1/2 rule in the Lambda N--> NN process. Due to the low
experimental precision, a possible violation of this rule can be neither proved
nor excluded at present with sufficient accuracy: a pure Delta I=1/2 transition
amplitude is excluded at 40% confidence level.
