Abstract: At several stages before and after infection by rust fungus ( Puccoda arachidcs ) .analysis was made of the activities of several enzymes, including phenylalanine ammonia lyase ( PAL). peroxida.se (PO) and polyphenodoxidase ( PPO), in five cultivars of peanut ( Arachis hypogaea Linn. ) with different levels of resistance, and their relationships to resistance. PAL was an induced enzyme, whose activity could only be observed after infection ,and was found to be positively related to resistance. The level of PO activity in infected plants was higher than that in healthy ones in most cultivars at 12,24,and 48 horus after infection, the more susceptible the cultivar.ihe more its change in infected plants. PPO activity in healthy plants was significantly related to resistance of the cultivars,but no relationship was found bwtween its activity and resistance in infected tissues.