The effect of some metal ions (Fe2+, Ni2+, Zn2+, Pb2+) upon the fluorescent intensity of a first generation polyamidoamine dendrimer with a peripheral 4-dimethylaminoethylamine-1,8-naphthalimide group was investigated. The presence of metal ions was found to evoke a photoinduced electron transfer leading to an enhancement in the fluorescence. The results obtained reveal the capacities of these systems to act as sensitive detectors of environment pollution by metal ions. The metal ions inhibit the photodegradation of the dendrimer molecule which exhibits PET properties.