Abstract
The length of the Pseudomonas aeruginosa filamentous bacteriophage Pf was found to be 1915 ± 77 nm, as measured in the electron microscope using the Kleinschmidt spreading technique. Pf is thus the longest filamentous phage so far isolated. Coliphage If, the I-specific filamentous phage, is nearest to it with a length of 1300 nm.