The response of 10 rubber (Hevea benthamiana) clones to 3 isolates of M. ulei (EB1, EB2 and MB1) from pathogenicity groups I and II was evaluated. The monocyclic parameters, i.e. incubation period, latent period, lesion size and reaction type, were studied. A conidial suspension of 2x10 5 conidia/ml was inoculated onto the abaxial leaflet surface in the B1/B2 stage; the seedlings were placed in a humid chamber for 24h at 24+_1 oC. The seedlings were then transferred into a growth chamber at the same temperature until the last evaluation at 15 days. Majority of the clones showed resistance to the 3 isolates. There was no significant interaction between clones and isolates in relation to incubation period, but there was a significant interaction between clones and isolates in relation to lesion diameter. The clones CNSAM 8218 and CNSAM 8219 were highly resistant and showed the smallest mean lesion diameter when inoculated with isolate EB1, while CNSAM 8219 also showed a small mean lesion when inoculated with isolate EB2. On the other hand, the clone CNSAM 8205 showed the largest mean lesion diameter when inoculated with EB1, CNSAM 8204 when inoculated with EB2 and MB1, and CNSAM 8201 when inoculated with EB2. These clones showed vertical resistance to M. ulei, makiing them unsuitable for the rubber breeding programme aimed to obtain clones with horizontal resistance to the pathogen.