The results of ELISA tests done on leaves, with or without symptoms, sampled in different areas of the canopy of trees affected by Sharka are reported. The results demonstrate that ELISA is not reliable for Plum pox virus (PPV) detection when asymptomatic leaves are used. Comparative analysis of different areas of the leaf blade indicates the possibility of improving the efficiency of the test. However, the definition of a more efficient sampling methodology needs further studies.