Abstract
The morphology and ultrastructure of Mycoplasmatales virus laidlawii 1, a new helical DNA virus, were studied by electron microscopy and optical diffractometry. Numerous small unenveloped rod-like particles and a few longer forms were seen in purified, concentrated preparations of infective virus, and associated with virus-infected mycoplasmal cells in culture. Observations on these virus particles are discussed in relation to their structure.