In the framework of the seesaw models with triplets of fermions, we evaluate the decay rates of $mu to e gamma$ and $tau to l gamma$ transitions. We show that although, due to neutrino mass constraints, those rates are in general expected to be well
under the present experimental limits, this is not necessarily always the case. Interestingly enough, the observation of one of those decays in planned experiments would nevertheless contradict bounds stemming from present experimental limits on the $mu to eee$ and $tau to 3 l$ decay rates. Such detection of radiative decays would therefore imply that there exist sources of lepton flavour violation not associated to triplet fermions.
