Instrumental neutron activation analysis was used to measure 17 elements in 2 families of leaves of tropical plants. The concentrations of most of the trace elements measured, especially toxic elements like As, Br, Cr, Hg, Sb and Zn, were found to correlate well with the polluted nature of the locations where the trees were grown and also with the age of the plants. It was observed that the trees used in this study could be used as bioindicators for the pollution state of the surrounding environment.