Various theoretical and experimental investigations have been carried out on double beta decay, and particularly on neutrinoless ββ decay as a very sensible way of testing lepton non conservation. This decay has been mostly considered, and its lifetime calculated, as the product of two ordinary beta decays (1–3). Recently however B. Pontecorvo (4) has considered the possibility of a “direct” superweak interaction with ΔL=2. Experiments based on direct methods of detection of the electrons (nuclear emulsions, cloud and spark chambers, counters) have given up to now no evidence for any type of decay (3,5). On the contrary evidence for ββ decay of 128Te and 130Te has been obtained with chemical and mass spectroscopic analysis of geological samples (6). This technique cannot however discriminate between neutrinoless and two neutrino decay; and possible background effects simulating ββ decay are hard to be excluded.