Irritant potential of 3 cacti, Opuntia dilenii, Rhispalis baccifera and Cereus Peruvians, and 4 succulents, Euphorbia royleana, Euphorbia antiquorum,Sansevieria zeyilanica and Agave sisalana was tested by rubbing their freshly exposed pulp 10 times on the forearm skin of 10 human voluntrees. Opuntia dilenii, Euphorbia antiquorum, Rhispalis baccifera and Agave sisalana produced transitory itching and burning or dermatitis in only one patient each, indicating that these plants are not highly irritant. Patch tests undertaken with the juice, pulp or other components of these plants as well as those of 5 lichens, Parmelia trichotera, Parmelia sulcata, Parmelia quercina, Parmelia furfuracea and Parmelia verrucifera, and 6 aquatic plants Nelumbo nucifera, Eichnornia crassipes, Trapa natans, Anabaena, Salvinia auriculata and Ceratophyllam demeusam in 10 cases each revealed positive reaction with Opuntia Dilenil, Rhispalis baccifera, Cereus Peruvians, Parmelia verrucifera, Nelumbo nucifera, Trapa natans, Salvinia auriculata and Ceratophyllum demeusum in one case each. Agava sisalana and Sensevieria zeylanica in 2 cases each. Euphorbia antiquorym, Parmelia trichotera ' Parmelia quercina, Parmelia furfuracea and Eichhornia crassipes in 3 cases each and Euphorbia royleana and Parmelia sulcata in 4 cases each.