Major advances have occurred the past few years in the cultivation of a number of new, fastidious mollicutes--events which can be traced directly to successful efforts to develop culture media for the expanding group of helical mollicutes (spiroplasmas) inhabiting plants and arthropods. A description of cultivation techniques successful in primary isolation of three unusual mollicutes, representing new mycoplasmas from man and animals and a new spiroplasma from ticks, emphasizes some important factors in recovery of wall-less prokaryotes with special cultural requirements. Vigorous efforts to understand the distribution of spiroplasmas in plant and insect hosts also led to the cultivation of new, non-helical mollicutes. Preliminary characterization of a number of these new agents offers strong evidence for a unique and distinct Acholeplasma and Mycoplasma flora of both plants and insects.