Assessing the diversity of the Trypanosomatidae is difficult because of the relatively small number of species that can be cultured. This same problem thwarts efforts to identify the hosts and insect vectors of Phytomonas, a genus of parasites of plants that includes species responsible for devastating epiphytotics of economically important plantations. Here, Myrna Serrano, Marta Teixeira and Erney Camargo review the studies that have led to the development of a PCR-based technique for processing insect and plant juices fixed on glass slides. The method overcomes the need for cultivation, facilitates field collections and also permits the molecular examination of archival smears of Phytomonas. In principle, the method can be adapted to any trypanosomatid as well as to any fastidious parasitic or free-living organism.