Several phytoplasmas have been associated with diseases of coconut palm (Cocos nucifera). Lethal yellowing diseases (LYD) (Fig. 1-2) of coconut have been endemic to Caribbean since the end of the 19th century, and to West Africa since 1900. However, diagnosis by electron microscopy has only been possible since the 1970s. Polymerase chain reaction (PCR) diagnosis is now routinely used. Two strategies allow the study of genetic variability in PCR products: RFLP with a set of restriction enzymes or sequencing, both of which require considerable time and expense. In this experience, heteroduplex mobility assay (HMA) was used.